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Appenders

Appenders are responsible for delivering LogEvents to their destination. Every Appender must implement the Appender interface. Most Appenders will extend AbstractAppender which adds Lifecycle and Filterable support. Lifecycle allows components to finish initialization after configuration has completed and to perform cleanup during shutdown. Filterable allows the component to have Filters attached to it which are evaluated during event processing.

Appenders usually are only responsible for writing the event data to the target destination. In most cases they delegate responsibility for formatting the event to a layout. Some appenders wrap other appenders so that they can modify the LogEvent, handle a failure in an Appender, route the event to a subordinate Appender based on advanced Filter criteria or provide similar functionality that does not directly format the event for viewing.

Appenders always have a name so that they can be referenced from Loggers.

In the tables below, the "Type" column corresponds to the Java type expected. For non-JDK classes, these should usually be in Log4j Core unless otherwise noted.

AsyncAppender

The AsyncAppender accepts references to other Appenders and causes LogEvents to be written to them on a separate Thread. Note that exceptions while writing to those Appenders will be hidden from the application. The AsyncAppender should be configured after the appenders it references to allow it to shut down properly.

By default, AsyncAppender uses java.util.concurrent.ArrayBlockingQueue which does not require any external libraries. Note that multi-threaded applications should exercise care when using this appender as such: the blocking queue is susceptible to lock contention and our tests showed performance may become worse when more threads are logging concurrently. Consider using lock-free Async Loggers for optimal performance.

AsyncAppender Parameters
Parameter Name Type Description
AppenderRef String The name of the Appenders to invoke asynchronously. Multiple AppenderRef elements can be configured.
blocking boolean If true, the appender will wait until there are free slots in the queue. If false, the event will be written to the error appender if the queue is full. The default is true.
shutdownTimeout integer How many milliseconds the Appender should wait to flush outstanding log events in the queue on shutdown. The default is zero which means to wait forever.
bufferSize integer Specifies the maximum number of events that can be queued. The default is 128. Note that when using a disruptor-style BlockingQueue, this buffer size must be a power of 2.
errorRef String The name of the Appender to invoke if none of the appenders can be called, either due to errors in the appenders or because the queue is full. If not specified then errors will be ignored.
filter Filter A Filter to determine if the event should be handled by this Appender. More than one Filter may be used by using a CompositeFilter.
name String The name of the Appender.
ignoreExceptions boolean The default is true, causing exceptions encountered while appending events to be internally logged and then ignored. When set to false exceptions will be propagated to the caller, instead. You must set this to false when wrapping this Appender in a FailoverAppender.
includeLocation boolean Extracting location is an expensive operation (it can make logging 5 - 20 times slower). To improve performance, location is not included by default when adding a log event to the queue. You can change this by setting includeLocation="true".
BlockingQueueFactory BlockingQueueFactory This element overrides what type of BlockingQueue to use. See below documentation for more details.

There are also a few system properties that can be used to maintain application throughput even when the underlying appender cannot keep up with the logging rate and the queue is filling up. See the details for system properties log4j2.AsyncQueueFullPolicy and log4j2.DiscardThreshold.

A typical AsyncAppender configuration might look like:

<?xml version="1.0" encoding="UTF-8"?>
<Configuration status="warn" name="MyApp" packages="">
  <Appenders>
    <File name="MyFile" fileName="logs/app.log">
      <PatternLayout>
        <Pattern>%d %p %c{1.} [%t] %m%n</Pattern>
      </PatternLayout>
    </File>
    <Async name="Async">
      <AppenderRef ref="MyFile"/>
    </Async>
  </Appenders>
  <Loggers>
    <Root level="error">
      <AppenderRef ref="Async"/>
    </Root>
  </Loggers>
</Configuration>

Starting in Log4j 2.7, a custom implementation of BlockingQueue or TransferQueue can be specified using a BlockingQueueFactory plugin. To override the default BlockingQueueFactory, specify the plugin inside an <Async/> element like so:

<Configuration name="LinkedTransferQueueExample">
  <Appenders>
    <List name="List"/>
    <Async name="Async" bufferSize="262144">
      <AppenderRef ref="List"/>
      <LinkedTransferQueue/>
    </Async>
  </Appenders>
  <Loggers>
    <Root>
      <AppenderRef ref="Async"/>
    </Root>
  </Loggers>
</Configuration>

Log4j ships with the following implementations:

BlockingQueueFactory Implementations
Plugin Name Description
ArrayBlockingQueue This is the default implementation that uses ArrayBlockingQueue.
DisruptorBlockingQueue This uses the Conversant Disruptor implementation of BlockingQueue. This plugin takes a single optional attribute, spinPolicy, which corresponds to
JCToolsBlockingQueue This uses JCTools, specifically the MPSC bounded lock-free queue.
LinkedTransferQueue This uses the new in Java 7 implementation LinkedTransferQueue. Note that this queue does not use the bufferSize configuration attribute from AsyncAppender as LinkedTransferQueue does not support a maximum capacity.

CassandraAppender

The CassandraAppender writes its output to an Apache Cassandra database. A keyspace and table must be configured ahead of time, and the columns of that table are mapped in a configuration file. Each column can specify either a StringLayout (e.g., a PatternLayout) along with an optional conversion type, or only a conversion type for org.apache.logging.log4j.spi.ThreadContextMap or org.apache.logging.log4j.spi.ThreadContextStack to store the MDC or NDC in a map or list column respectively. A conversion type compatible with java.util.Date will use the log event timestamp converted to that type (e.g., use java.util.Date to fill a timestamp column type in Cassandra).

CassandraAppender Parameters
Parameter Name Type Description
batched boolean Whether or not to use batch statements to write log messages to Cassandra. By default, this is false.
batchType BatchStatement.Type The batch type to use when using batched writes. By default, this is LOGGED.
bufferSize int The number of log messages to buffer or batch before writing. By default, no buffering is done.
clusterName String The name of the Cassandra cluster to connect to.
columns ColumnMapping[] A list of column mapping configurations. Each column must specify a column name. Each column can have a conversion type specified by its fully qualified class name. By default, the conversion type is String. If the configured type is assignment-compatible with ReadOnlyStringMap / ThreadContextMap or ThreadContextStack, then that column will be populated with the MDC or NDC respectively. If the configured type is assignment-compatible with java.util.Date, then the log timestamp will be converted to that configured date type. If a literal attribute is given, then its value will be used as is in the INSERT query without any escaping. Otherwise, the layout or pattern specified will be converted into the configured type and stored in that column.
contactPoints SocketAddress[] A list of hosts and ports of Cassandra nodes to connect to. These must be valid hostnames or IP addresses. By default, if a port is not specified for a host or it is set to 0, then the default Cassandra port of 9042 will be used. By default, localhost:9042 will be used.
filter Filter A Filter to determine if the event should be handled by this Appender. More than one Filter may be used by using a CompositeFilter.
ignoreExceptions boolean The default is true, causing exceptions encountered while appending events to be internally logged and then ignored. When set to false exceptions will be propagated to the caller, instead. You must set this to false when wrapping this Appender in a FailoverAppender.
keyspace String The name of the keyspace containing the table that log messages will be written to.
name String The name of the Appender.
password String The password to use (along with the username) to connect to Cassandra.
table String The name of the table to write log messages to.
useClockForTimestampGenerator boolean Whether or not to use the configured org.apache.logging.log4j.core.util.Clock as a TimestampGenerator. By default, this is false.
username String The username to use to connect to Cassandra. By default, no username or password is used.
useTls boolean Whether or not to use TLS/SSL to connect to Cassandra. This is false by default.

Here is an example CassandraAppender configuration:

<Configuration name="CassandraAppenderTest">
  <Appenders>
    <Cassandra name="Cassandra" clusterName="Test Cluster" keyspace="test" table="logs" bufferSize="10" batched="true">
      <SocketAddress host="localhost" port="9042"/>
      <ColumnMapping name="id" pattern="%uuid{TIME}" type="java.util.UUID"/>
      <ColumnMapping name="timeid" literal="now()"/>
      <ColumnMapping name="message" pattern="%message"/>
      <ColumnMapping name="level" pattern="%level"/>
      <ColumnMapping name="marker" pattern="%marker"/>
      <ColumnMapping name="logger" pattern="%logger"/>
      <ColumnMapping name="timestamp" type="java.util.Date"/>
      <ColumnMapping name="mdc" type="org.apache.logging.log4j.spi.ThreadContextMap"/>
      <ColumnMapping name="ndc" type="org.apache.logging.log4j.spi.ThreadContextStack"/>
    </Cassandra>
  </Appenders>
  <Loggers>
    <Logger name="org.apache.logging.log4j.nosql.appender.cassandra" level="DEBUG">
      <AppenderRef ref="Cassandra"/>
    </Logger>
    <Root level="ERROR"/>
  </Loggers>
</Configuration>

This example configuration uses the following table schema:

CREATE TABLE logs (
    id timeuuid PRIMARY KEY,
    timeid timeuuid,
    message text,
    level text,
    marker text,
    logger text,
    timestamp timestamp,
    mdc map<text,text>,
    ndc list<text>
);

ConsoleAppender

As one might expect, the ConsoleAppender writes its output to either System.out or System.err with System.out being the default target. A Layout must be provided to format the LogEvent.

ConsoleAppender Parameters
Parameter Name Type Description
filter Filter A Filter to determine if the event should be handled by this Appender. More than one Filter may be used by using a CompositeFilter.
layout Layout The Layout to use to format the LogEvent. If no layout is supplied the default pattern layout of "%m%n" will be used.
follow boolean Identifies whether the appender honors reassignments of System.out or System.err via System.setOut or System.setErr made after configuration. Note that the follow attribute cannot be used with Jansi on Windows. Cannot be used with direct.
direct boolean Write directly to java.io.FileDescriptor and bypass java.lang.System.out/.err. Can give up to 10x performance boost when the output is redirected to file or other process. Cannot be used with Jansi on Windows. Cannot be used with follow. Output will not respect java.lang.System.setOut()/.setErr() and may get intertwined with other output to java.lang.System.out/.err in a multi-threaded application. New since 2.6.2. Be aware that this is a new addition, and it has only been tested with Oracle JVM on Linux and Windows so far.
name String The name of the Appender.
ignoreExceptions boolean The default is true, causing exceptions encountered while appending events to be internally logged and then ignored. When set to false exceptions will be propagated to the caller, instead. You must set this to false when wrapping this Appender in a FailoverAppender.
target String Either "SYSTEM_OUT" or "SYSTEM_ERR". The default is "SYSTEM_OUT".

A typical Console configuration might look like:

<?xml version="1.0" encoding="UTF-8"?>
<Configuration status="warn" name="MyApp" packages="">
  <Appenders>
    <Console name="STDOUT" target="SYSTEM_OUT">
      <PatternLayout pattern="%m%n"/>
    </Console>
  </Appenders>
  <Loggers>
    <Root level="error">
      <AppenderRef ref="STDOUT"/>
    </Root>
  </Loggers>
</Configuration>

FailoverAppender

The FailoverAppender wraps a set of appenders. If the primary Appender fails the secondary appenders will be tried in order until one succeeds or there are no more secondaries to try.

FailoverAppender Parameters
Parameter Name Type Description
filter Filter A Filter to determine if the event should be handled by this Appender. More than one Filter may be used by using a CompositeFilter.
primary String The name of the primary Appender to use.
failovers String[] The names of the secondary Appenders to use.
name String The name of the Appender.
retryIntervalSeconds integer The number of seconds that should pass before retrying the primary Appender. The default is 60.
ignoreExceptions boolean The default is true, causing exceptions encountered while appending events to be internally logged and then ignored. When set to false exceptions will be propagated to the caller, instead.
target String Either "SYSTEM_OUT" or "SYSTEM_ERR". The default is "SYSTEM_ERR".

A Failover configuration might look like:

<?xml version="1.0" encoding="UTF-8"?>
<Configuration status="warn" name="MyApp" packages="">
  <Appenders>
    <RollingFile name="RollingFile" fileName="logs/app.log" filePattern="logs/app-%d{MM-dd-yyyy}.log.gz"
                 ignoreExceptions="false">
      <PatternLayout>
        <Pattern>%d %p %c{1.} [%t] %m%n</Pattern>
      </PatternLayout>
      <TimeBasedTriggeringPolicy />
    </RollingFile>
    <Console name="STDOUT" target="SYSTEM_OUT" ignoreExceptions="false">
      <PatternLayout pattern="%m%n"/>
    </Console>
    <Failover name="Failover" primary="RollingFile">
      <Failovers>
        <AppenderRef ref="Console"/>
      </Failovers>
    </Failover>
  </Appenders>
  <Loggers>
    <Root level="error">
      <AppenderRef ref="Failover"/>
    </Root>
  </Loggers>
</Configuration>

FileAppender

The FileAppender is an OutputStreamAppender that writes to the File named in the fileName parameter. The FileAppender uses a FileManager (which extends OutputStreamManager) to actually perform the file I/O. While FileAppenders from different Configurations cannot be shared, the FileManagers can be if the Manager is accessible. For example, two web applications in a servlet container can have their own configuration and safely write to the same file if Log4j is in a ClassLoader that is common to both of them.

FileAppender Parameters
Parameter Name Type Description
append boolean When true - the default, records will be appended to the end of the file. When set to false, the file will be cleared before new records are written.
bufferedIO boolean When true - the default, records will be written to a buffer and the data will be written to disk when the buffer is full or, if immediateFlush is set, when the record is written. File locking cannot be used with bufferedIO. Performance tests have shown that using buffered I/O significantly improves performance, even if immediateFlush is enabled.
bufferSize int When bufferedIO is true, this is the buffer size, the default is 8192 bytes.
createOnDemand boolean The appender creates the file on-demand. The appender only creates the file when a log event passes all filters and is routed to this appender. Defaults to false.
filter Filter A Filter to determine if the event should be handled by this Appender. More than one Filter may be used by using a CompositeFilter.
fileName String The name of the file to write to. If the file, or any of its parent directories, do not exist, they will be created.
immediateFlush boolean

When set to true - the default, each write will be followed by a flush. This will guarantee the data is written to disk but could impact performance.

Flushing after every write is only useful when using this appender with synchronous loggers. Asynchronous loggers and appenders will automatically flush at the end of a batch of events, even if immediateFlush is set to false. This also guarantees the data is written to disk but is more efficient.

layout Layout The Layout to use to format the LogEvent. If no layout is supplied the default pattern layout of "%m%n" will be used.
locking boolean When set to true, I/O operations will occur only while the file lock is held allowing FileAppenders in multiple JVMs and potentially multiple hosts to write to the same file simultaneously. This will significantly impact performance so should be used carefully. Furthermore, on many systems the file lock is "advisory" meaning that other applications can perform operations on the file without acquiring a lock. The default value is false.
name String The name of the Appender.
ignoreExceptions boolean The default is true, causing exceptions encountered while appending events to be internally logged and then ignored. When set to false exceptions will be propagated to the caller, instead. You must set this to false when wrapping this Appender in a FailoverAppender.

Here is a sample File configuration:

<?xml version="1.0" encoding="UTF-8"?>
<Configuration status="warn" name="MyApp" packages="">
  <Appenders>
    <File name="MyFile" fileName="logs/app.log">
      <PatternLayout>
        <Pattern>%d %p %c{1.} [%t] %m%n</Pattern>
      </PatternLayout>
    </File>
  </Appenders>
  <Loggers>
    <Root level="error">
      <AppenderRef ref="MyFile"/>
    </Root>
  </Loggers>
</Configuration>

FlumeAppender

This is an optional component supplied in a separate jar.

Apache Flume is a distributed, reliable, and available system for efficiently collecting, aggregating, and moving large amounts of log data from many different sources to a centralized data store. The FlumeAppender takes LogEvents and sends them to a Flume agent as serialized Avro events for consumption.

The Flume Appender supports three modes of operation.

  1. It can act as a remote Flume client which sends Flume events via Avro to a Flume Agent configured with an Avro Source.
  2. It can act as an embedded Flume Agent where Flume events pass directly into Flume for processing.
  3. It can persist events to a local BerkeleyDB data store and then asynchronously send the events to Flume, similar to the embedded Flume Agent but without most of the Flume dependencies.

Usage as an embedded agent will cause the messages to be directly passed to the Flume Channel and then control will be immediately returned to the application. All interaction with remote agents will occur asynchronously. Setting the "type" attribute to "Embedded" will force the use of the embedded agent. In addition, configuring agent properties in the appender configuration will also cause the embedded agent to be used.

FlumeAppender Parameters
Parameter Name Type Description
agents Agent[] An array of Agents to which the logging events should be sent. If more than one agent is specified the first Agent will be the primary and subsequent Agents will be used in the order specified as secondaries should the primary Agent fail. Each Agent definition supplies the Agents host and port. The specification of agents and properties are mutually exclusive. If both are configured an error will result.
agentRetries integer The number of times the agent should be retried before failing to a secondary. This parameter is ignored when type="persistent" is specified (agents are tried once before failing to the next).
batchSize integer Specifies the number of events that should be sent as a batch. The default is 1. This parameter only applies to the Flume Appender.
compress boolean When set to true the message body will be compressed using gzip
connectTimeoutMillis integer The number of milliseconds Flume will wait before timing out the connection.
dataDir String Directory where the Flume write ahead log should be written. Valid only when embedded is set to true and Agent elements are used instead of Property elements.
filter Filter A Filter to determine if the event should be handled by this Appender. More than one Filter may be used by using a CompositeFilter.
eventPrefix String The character string to prepend to each event attribute in order to distinguish it from MDC attributes. The default is an empty string.
flumeEventFactory FlumeEventFactory Factory that generates the Flume events from Log4j events. The default factory is the FlumeAvroAppender itself.
layout Layout The Layout to use to format the LogEvent. If no layout is specified RFC5424Layout will be used.
lockTimeoutRetries integer The number of times to retry if a LockConflictException occurs while writing to Berkeley DB. The default is 5.
maxDelayMillis integer The maximum number of milliseconds to wait for batchSize events before publishing the batch.
mdcExcludes String A comma separated list of mdc keys that should be excluded from the FlumeEvent. This is mutually exclusive with the mdcIncludes attribute.
mdcIncludes String A comma separated list of mdc keys that should be included in the FlumeEvent. Any keys in the MDC not found in the list will be excluded. This option is mutually exclusive with the mdcExcludes attribute.
mdcRequired String A comma separated list of mdc keys that must be present in the MDC. If a key is not present a LoggingException will be thrown.
mdcPrefix String A string that should be prepended to each MDC key in order to distinguish it from event attributes. The default string is "mdc:".
name String The name of the Appender.
properties Property[]

One or more Property elements that are used to configure the Flume Agent. The properties must be configured without the agent name (the appender name is used for this) and no sources can be configured. Interceptors can be specified for the source using "sources.log4j-source.interceptors". All other Flume configuration properties are allowed. Specifying both Agent and Property elements will result in an error.

When used to configure in Persistent mode the valid properties are:

  1. "keyProvider" to specify the name of the plugin to provide the secret key for encryption.
requestTimeoutMillis integer The number of milliseconds Flume will wait before timing out the request.
ignoreExceptions boolean The default is true, causing exceptions encountered while appending events to be internally logged and then ignored. When set to false exceptions will be propagated to the caller, instead. You must set this to false when wrapping this Appender in a FailoverAppender.
type enumeration One of "Avro", "Embedded", or "Persistent" to indicate which variation of the Appender is desired.

A sample FlumeAppender configuration that is configured with a primary and a secondary agent, compresses the body, and formats the body using the RFC5424Layout:

<?xml version="1.0" encoding="UTF-8"?>
<Configuration status="warn" name="MyApp" packages="">
  <Appenders>
    <Flume name="eventLogger" compress="true">
      <Agent host="192.168.10.101" port="8800"/>
      <Agent host="192.168.10.102" port="8800"/>
      <RFC5424Layout enterpriseNumber="18060" includeMDC="true" appName="MyApp"/>
    </Flume>
  </Appenders>
  <Loggers>
    <Root level="error">
      <AppenderRef ref="eventLogger"/>
    </Root>
  </Loggers>
</Configuration>

A sample FlumeAppender configuration that is configured with a primary and a secondary agent, compresses the body, formats the body using the RFC5424Layout, and persists encrypted events to disk:

<?xml version="1.0" encoding="UTF-8"?>
<Configuration status="warn" name="MyApp" packages="">
  <Appenders>
    <Flume name="eventLogger" compress="true" type="persistent" dataDir="./logData">
      <Agent host="192.168.10.101" port="8800"/>
      <Agent host="192.168.10.102" port="8800"/>
      <RFC5424Layout enterpriseNumber="18060" includeMDC="true" appName="MyApp"/>
      <Property name="keyProvider">MySecretProvider</Property>
    </Flume>
  </Appenders>
  <Loggers>
    <Root level="error">
      <AppenderRef ref="eventLogger"/>
    </Root>
  </Loggers>
</Configuration>

A sample FlumeAppender configuration that is configured with a primary and a secondary agent, compresses the body, formats the body using RFC5424Layout and passes the events to an embedded Flume Agent.

<?xml version="1.0" encoding="UTF-8"?>
<Configuration status="warn" name="MyApp" packages="">
  <Appenders>
    <Flume name="eventLogger" compress="true" type="Embedded">
      <Agent host="192.168.10.101" port="8800"/>
      <Agent host="192.168.10.102" port="8800"/>
      <RFC5424Layout enterpriseNumber="18060" includeMDC="true" appName="MyApp"/>
    </Flume>
    <Console name="STDOUT">
      <PatternLayout pattern="%d [%p] %c %m%n"/>
    </Console>
  </Appenders>
  <Loggers>
    <Logger name="EventLogger" level="info">
      <AppenderRef ref="eventLogger"/>
    </Logger>
    <Root level="warn">
      <AppenderRef ref="STDOUT"/>
    </Root>
  </Loggers>
</Configuration>

A sample FlumeAppender configuration that is configured with a primary and a secondary agent using Flume configuration properties, compresses the body, formats the body using RFC5424Layout and passes the events to an embedded Flume Agent.

<?xml version="1.0" encoding="UTF-8"?>
<Configuration status="error" name="MyApp" packages="">
  <Appenders>
    <Flume name="eventLogger" compress="true" type="Embedded">
      <Property name="channels">file</Property>
      <Property name="channels.file.type">file</Property>
      <Property name="channels.file.checkpointDir">target/file-channel/checkpoint</Property>
      <Property name="channels.file.dataDirs">target/file-channel/data</Property>
      <Property name="sinks">agent1 agent2</Property>
      <Property name="sinks.agent1.channel">file</Property>
      <Property name="sinks.agent1.type">avro</Property>
      <Property name="sinks.agent1.hostname">192.168.10.101</Property>
      <Property name="sinks.agent1.port">8800</Property>
      <Property name="sinks.agent1.batch-size">100</Property>
      <Property name="sinks.agent2.channel">file</Property>
      <Property name="sinks.agent2.type">avro</Property>
      <Property name="sinks.agent2.hostname">192.168.10.102</Property>
      <Property name="sinks.agent2.port">8800</Property>
      <Property name="sinks.agent2.batch-size">100</Property>
      <Property name="sinkgroups">group1</Property>
      <Property name="sinkgroups.group1.sinks">agent1 agent2</Property>
      <Property name="sinkgroups.group1.processor.type">failover</Property>
      <Property name="sinkgroups.group1.processor.priority.agent1">10</Property>
      <Property name="sinkgroups.group1.processor.priority.agent2">5</Property>
      <RFC5424Layout enterpriseNumber="18060" includeMDC="true" appName="MyApp"/>
    </Flume>
    <Console name="STDOUT">
      <PatternLayout pattern="%d [%p] %c %m%n"/>
    </Console>
  </Appenders>
  <Loggers>
    <Logger name="EventLogger" level="info">
      <AppenderRef ref="eventLogger"/>
    </Logger>
    <Root level="warn">
      <AppenderRef ref="STDOUT"/>
    </Root>
  </Loggers>
</Configuration>

JDBCAppender

The JDBCAppender writes log events to a relational database table using standard JDBC. It can be configured to obtain JDBC connections using a JNDI DataSource or a custom factory method. Whichever approach you take, it must be backed by a connection pool. Otherwise, logging performance will suffer greatly. If batch statements are supported by the configured JDBC driver and a bufferSize is configured to be a positive number, then log events will be batched. Note that as of Log4j 2.8, there are two ways to configure log event to column mappings: the original ColumnConfig style that only allows strings and timestamps, and the new ColumnMapping plugin that uses Log4j's built-in type conversion to allow for more data types (this is the same plugin as in the Cassandra Appender).

JDBCAppender Parameters
Parameter Name Type Description
name String Required. The name of the Appender.
ignoreExceptions boolean The default is true, causing exceptions encountered while appending events to be internally logged and then ignored. When set to false exceptions will be propagated to the caller, instead. You must set this to false when wrapping this Appender in a FailoverAppender.
filter Filter A Filter to determine if the event should be handled by this Appender. More than one Filter may be used by using a CompositeFilter.
bufferSize int If an integer greater than 0, this causes the appender to buffer log events and flush whenever the buffer reaches this size.
connectionSource ConnectionSource Required. The connections source from which database connections should be retrieved.
tableName String Required. The name of the database table to insert log events into.
columnConfigs ColumnConfig[] Required (and/or columnMappings). Information about the columns that log event data should be inserted into and how to insert that data. This is represented with multiple <Column> elements.
columnMappings ColumnMapping[] Required (and/or columnConfigs). A list of column mapping configurations. Each column must specify a column name. Each column can have a conversion type specified by its fully qualified class name. By default, the conversion type is String. If the configured type is assignment-compatible with ReadOnlyStringMap / ThreadContextMap or ThreadContextStack, then that column will be populated with the MDC or NDC respectively (this is database-specific how they handle inserting a Map or List value). If the configured type is assignment-compatible with java.util.Date, then the log timestamp will be converted to that configured date type. If the configured type is assignment-compatible with java.sql.Clob or java.sql.NClob, then the formatted event will be set as a Clob or NClob respectively (similar to the traditional ColumnConfig plugin). If a literal attribute is given, then its value will be used as is in the INSERT query without any escaping. Otherwise, the layout or pattern specified will be converted into the configured type and stored in that column.

When configuring the JDBCAppender, you must specify a ConnectionSource implementation from which the Appender gets JDBC connections. You must use exactly one of the <DataSource> or <ConnectionFactory> nested elements.

DataSource Parameters
Parameter Name Type Description
jndiName String Required. The full, prefixed JNDI name that the javax.sql.DataSource is bound to, such as java:/comp/env/jdbc/LoggingDatabase. The DataSource must be backed by a connection pool; otherwise, logging will be very slow.
ConnectionFactory Parameters
Parameter Name Type Description
class Class Required. The fully qualified name of a class containing a static factory method for obtaining JDBC connections.
method Method Required. The name of a static factory method for obtaining JDBC connections. This method must have no parameters and its return type must be either java.sql.Connection or DataSource. If the method returns Connections, it must obtain them from a connection pool (and they will be returned to the pool when Log4j is done with them); otherwise, logging will be very slow. If the method returns a DataSource, the DataSource will only be retrieved once, and it must be backed by a connection pool for the same reasons.

When configuring the JDBCAppender, use the nested <Column> elements to specify which columns in the table should be written to and how to write to them. The JDBCAppender uses this information to formulate a PreparedStatement to insert records without SQL injection vulnerability.

Column Parameters
Parameter Name Type Description
name String Required. The name of the database column.
pattern String Use this attribute to insert a value or values from the log event in this column using a PatternLayout pattern. Simply specify any legal pattern in this attribute. Either this attribute, literal, or isEventTimestamp="true" must be specified, but not more than one of these.
literal String Use this attribute to insert a literal value in this column. The value will be included directly in the insert SQL, without any quoting (which means that if you want this to be a string, your value should contain single quotes around it like this: literal="'Literal String'"). This is especially useful for databases that don't support identity columns. For example, if you are using Oracle you could specify literal="NAME_OF_YOUR_SEQUENCE.NEXTVAL" to insert a unique ID in an ID column. Either this attribute, pattern, or isEventTimestamp="true" must be specified, but not more than one of these.
isEventTimestamp boolean Use this attribute to insert the event timestamp in this column, which should be a SQL datetime. The value will be inserted as a java.sql.Types.TIMESTAMP. Either this attribute (equal to true), pattern, or isEventTimestamp must be specified, but not more than one of these.
isUnicode boolean This attribute is ignored unless pattern is specified. If true or omitted (default), the value will be inserted as unicode (setNString or setNClob). Otherwise, the value will be inserted non-unicode (setString or setClob).
isClob boolean This attribute is ignored unless pattern is specified. Use this attribute to indicate that the column stores Character Large Objects (CLOBs). If true, the value will be inserted as a CLOB (setClob or setNClob). If false or omitted (default), the value will be inserted as a VARCHAR or NVARCHAR (setString or setNString).

Here are a couple sample configurations for the JDBCAppender, as well as a sample factory implementation that uses Commons Pooling and Commons DBCP to pool database connections:

<?xml version="1.0" encoding="UTF-8"?>
<Configuration status="error">
  <Appenders>
    <JDBC name="databaseAppender" tableName="dbo.application_log">
      <DataSource jndiName="java:/comp/env/jdbc/LoggingDataSource" />
      <Column name="eventDate" isEventTimestamp="true" />
      <Column name="level" pattern="%level" />
      <Column name="logger" pattern="%logger" />
      <Column name="message" pattern="%message" />
      <Column name="exception" pattern="%ex{full}" />
    </JDBC>
  </Appenders>
  <Loggers>
    <Root level="warn">
      <AppenderRef ref="databaseAppender"/>
    </Root>
  </Loggers>
</Configuration>
<?xml version="1.0" encoding="UTF-8"?>
<Configuration status="error">
  <Appenders>
    <JDBC name="databaseAppender" tableName="LOGGING.APPLICATION_LOG">
      <ConnectionFactory class="net.example.db.ConnectionFactory" method="getDatabaseConnection" />
      <Column name="EVENT_ID" literal="LOGGING.APPLICATION_LOG_SEQUENCE.NEXTVAL" />
      <Column name="EVENT_DATE" isEventTimestamp="true" />
      <Column name="LEVEL" pattern="%level" />
      <Column name="LOGGER" pattern="%logger" />
      <Column name="MESSAGE" pattern="%message" />
      <Column name="THROWABLE" pattern="%ex{full}" />
    </JDBC>
  </Appenders>
  <Loggers>
    <Root level="warn">
      <AppenderRef ref="databaseAppender"/>
    </Root>
  </Loggers>
</Configuration>
package net.example.db;

import java.sql.Connection;
import java.sql.SQLException;
import java.util.Properties;

import javax.sql.DataSource;

import org.apache.commons.dbcp.DriverManagerConnectionFactory;
import org.apache.commons.dbcp.PoolableConnection;
import org.apache.commons.dbcp.PoolableConnectionFactory;
import org.apache.commons.dbcp.PoolingDataSource;
import org.apache.commons.pool.impl.GenericObjectPool;

public class ConnectionFactory {
    private static interface Singleton {
        final ConnectionFactory INSTANCE = new ConnectionFactory();
    }

    private final DataSource dataSource;

    private ConnectionFactory() {
        Properties properties = new Properties();
        properties.setProperty("user", "logging");
        properties.setProperty("password", "abc123"); // or get properties from some configuration file

        GenericObjectPool<PoolableConnection> pool = new GenericObjectPool<PoolableConnection>();
        DriverManagerConnectionFactory connectionFactory = new DriverManagerConnectionFactory(
                "jdbc:mysql://example.org:3306/exampleDb", properties
        );
        new PoolableConnectionFactory(
                connectionFactory, pool, null, "SELECT 1", 3, false, false, Connection.TRANSACTION_READ_COMMITTED
        );

        this.dataSource = new PoolingDataSource(pool);
    }

    public static Connection getDatabaseConnection() throws SQLException {
        return Singleton.INSTANCE.dataSource.getConnection();
    }
}

JMSAppender

The JMSAppender sends the formatted log event to a JMS Destination.

Note that in Log4j 2.0, this appender was split into a JMSQueueAppender and a JMSTopicAppender. Starting in Log4j 2.1, these appenders were combined into the JMSAppender which makes no distinction between queues and topics. However, configurations written for 2.0 which use the <JMSQueue/> or <JMSTopic/> elements will continue to work with the new <JMS/> configuration element.

JMSAppender Parameters
Parameter Name Type Description
factoryBindingName String The name to locate in the Context that provides the ConnectionFactory. This can be any subinterface of ConnectionFactory as well. This attribute is required.
factoryName String The fully qualified class name that should be used to define the Initial Context Factory as defined in INITIAL_CONTEXT_FACTORY. If no value is provided the default InitialContextFactory will be used. If a factoryName is specified without a providerURL a warning message will be logged as this is likely to cause problems.
filter Filter A Filter to determine if the event should be handled by this Appender. More than one Filter may be used by using a CompositeFilter.
layout Layout The Layout to use to format the LogEvent. If you do not specify a layout, this appender will use a SerializedLayout.
name String The name of the Appender. Required.
password String The password to use to create the JMS connection.
providerURL String The URL of the provider to use as defined by PROVIDER_URL. If this value is null the default system provider will be used.
destinationBindingName String The name to use to locate the Destination. This can be a Queue or Topic, and as such, the attribute names queueBindingName and topicBindingName are aliases to maintain compatibility with the Log4j 2.0 JMS appenders.
securityPrincipalName String The name of the identity of the Principal as specified by SECURITY_PRINCIPAL. If a securityPrincipalName is specified without securityCredentials a warning message will be logged as this is likely to cause problems.
securityCredentials String The security credentials for the principal as specified by SECURITY_CREDENTIALS.
ignoreExceptions boolean The default is true, causing exceptions encountered while appending events to be internally logged and then ignored. When set to false exceptions will be propagated to the caller, instead. You must set this to false when wrapping this Appender in a FailoverAppender.
urlPkgPrefixes String A colon-separated list of package prefixes for the class name of the factory class that will create a URL context factory as defined by URL_PKG_PREFIXES.
userName String The user id used to create the JMS connection.

Here is a sample JMSAppender configuration:

<?xml version="1.0" encoding="UTF-8"?>
<Configuration status="warn" name="MyApp">
  <Appenders>
    <JMS name="jmsQueue" destinationBindingName="MyQueue"
         factoryBindingName="MyQueueConnectionFactory"/>
  </Appenders>
  <Loggers>
    <Root level="error">
      <AppenderRef ref="jmsQueue"/>
    </Root>
  </Loggers>
</Configuration>

JPAAppender

The JPAAppender writes log events to a relational database table using the Java Persistence API 2.1. It requires the API and a provider implementation be on the classpath. It also requires a decorated entity configured to persist to the table desired. The entity should either extend org.apache.logging.log4j.core.appender.db.jpa.BasicLogEventEntity (if you mostly want to use the default mappings) and provide at least an @Id property, or org.apache.logging.log4j.core.appender.db.jpa.AbstractLogEventWrapperEntity (if you want to significantly customize the mappings). See the Javadoc for these two classes for more information. You can also consult the source code of these two classes as an example of how to implement the entity.

JPAAppender Parameters
Parameter Name Type Description
name String Required. The name of the Appender.
ignoreExceptions boolean The default is true, causing exceptions encountered while appending events to be internally logged and then ignored. When set to false exceptions will be propagated to the caller, instead. You must set this to false when wrapping this Appender in a FailoverAppender.
filter Filter A Filter to determine if the event should be handled by this Appender. More than one Filter may be used by using a CompositeFilter.
bufferSize int If an integer greater than 0, this causes the appender to buffer log events and flush whenever the buffer reaches this size.
entityClassName String Required. The fully qualified name of the concrete LogEventWrapperEntity implementation that has JPA annotations mapping it to a database table.
persistenceUnitName String Required. The name of the JPA persistence unit that should be used for persisting log events.

Here is a sample configuration for the JPAAppender. The first XML sample is the Log4j configuration file, the second is the persistence.xml file. EclipseLink is assumed here, but any JPA 2.1 or higher provider will do. You should always create a separate persistence unit for logging, for two reasons. First, <shared-cache-mode> must be set to "NONE," which is usually not desired in normal JPA usage. Also, for performance reasons the logging entity should be isolated in its own persistence unit away from all other entities and you should use a non-JTA data source. Note that your persistence unit must also contain <class> elements for all of the org.apache.logging.log4j.core.appender.db.jpa.converter converter classes.

<?xml version="1.0" encoding="UTF-8"?>
<Configuration status="error">
  <Appenders>
    <JPA name="databaseAppender" persistenceUnitName="loggingPersistenceUnit"
         entityClassName="com.example.logging.JpaLogEntity" />
  </Appenders>
  <Loggers>
    <Root level="warn">
      <AppenderRef ref="databaseAppender"/>
    </Root>
  </Loggers>
</Configuration>
<?xml version="1.0" encoding="UTF-8"?>
<persistence xmlns="http://xmlns.jcp.org/xml/ns/persistence"
             xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
             xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/persistence
                                 http://xmlns.jcp.org/xml/ns/persistence/persistence_2_1.xsd"
             version="2.1">

  <persistence-unit name="loggingPersistenceUnit" transaction-type="RESOURCE_LOCAL">
    <provider>org.eclipse.persistence.jpa.PersistenceProvider</provider>
    <class>org.apache.logging.log4j.core.appender.db.jpa.converter.ContextMapAttributeConverter</class>
    <class>org.apache.logging.log4j.core.appender.db.jpa.converter.ContextMapJsonAttributeConverter</class>
    <class>org.apache.logging.log4j.core.appender.db.jpa.converter.ContextStackAttributeConverter</class>
    <class>org.apache.logging.log4j.core.appender.db.jpa.converter.ContextStackJsonAttributeConverter</class>
    <class>org.apache.logging.log4j.core.appender.db.jpa.converter.MarkerAttributeConverter</class>
    <class>org.apache.logging.log4j.core.appender.db.jpa.converter.MessageAttributeConverter</class>
    <class>org.apache.logging.log4j.core.appender.db.jpa.converter.StackTraceElementAttributeConverter</class>
    <class>org.apache.logging.log4j.core.appender.db.jpa.converter.ThrowableAttributeConverter</class>
    <class>com.example.logging.JpaLogEntity</class>
    <non-jta-data-source>jdbc/LoggingDataSource</non-jta-data-source>
    <shared-cache-mode>NONE</shared-cache-mode>
  </persistence-unit>

</persistence>
package com.example.logging;
...
@Entity
@Table(name="application_log", schema="dbo")
public class JpaLogEntity extends BasicLogEventEntity {
    private static final long serialVersionUID = 1L;
    private long id = 0L;

    public TestEntity() {
        super(null);
    }
    public TestEntity(LogEvent wrappedEvent) {
        super(wrappedEvent);
    }

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Column(name = "id")
    public long getId() {
        return this.id;
    }

    public void setId(long id) {
        this.id = id;
    }

    // If you want to override the mapping of any properties mapped in BasicLogEventEntity,
    // just override the getters and re-specify the annotations.
}
package com.example.logging;
...
@Entity
@Table(name="application_log", schema="dbo")
public class JpaLogEntity extends AbstractLogEventWrapperEntity {
    private static final long serialVersionUID = 1L;
    private long id = 0L;

    public TestEntity() {
        super(null);
    }
    public TestEntity(LogEvent wrappedEvent) {
        super(wrappedEvent);
    }

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Column(name = "logEventId")
    public long getId() {
        return this.id;
    }

    public void setId(long id) {
        this.id = id;
    }

    @Override
    @Enumerated(EnumType.STRING)
    @Column(name = "level")
    public Level getLevel() {
        return this.getWrappedEvent().getLevel();
    }

    @Override
    @Column(name = "logger")
    public String getLoggerName() {
        return this.getWrappedEvent().getLoggerName();
    }

    @Override
    @Column(name = "message")
    @Convert(converter = MyMessageConverter.class)
    public Message getMessage() {
        return this.getWrappedEvent().getMessage();
    }
    ...
}

KafkaAppender

The KafkaAppender logs events to an Apache Kafka topic. Each log event is sent as a Kafka record with no key.

KafkaAppender Parameters
Parameter Name Type Description
topic String The Kafka topic to use. Required.
filter Filter A Filter to determine if the event should be handled by this Appender. More than one Filter may be used by using a CompositeFilter.
layout Layout The Layout to use to format the LogEvent. If you do not specify a layout, the appender will send the formatted message to Kafka as a UTF-8 encoded string.
name String The name of the Appender. Required.
ignoreExceptions boolean The default is true, causing exceptions encountered while appending events to be internally logged and then ignored. When set to false exceptions will be propagated to the caller, instead. You must set this to false when wrapping this Appender in a FailoverAppender.
syncSend boolean The default is true, causing sends to block until the record has been acknowledged by the Kafka server. When set to false sends return immediately, allowing for lower latency and significantly higher throughput. Note: This parameter is new since 2.8. Be aware that this is a new addition, and it has not been extensively tested. Any failure sending to Kafka will be ignored and the log event will be dropped (and the ignoreExceptions parameter will not be effective). Log events may arrive out of order to the Kafka server.
properties Property[] You can set properties in Kafka producer properties. You need to set the bootstrap.servers property, there are sensible default values for the others. Do not set the value.serializer property.

Here is a sample KafkaAppender configuration snippet:

<?xml version="1.0" encoding="UTF-8"?>
  ...
  <Appenders>
    <Kafka name="Kafka" topic="log-test">
      <PatternLayout pattern="%date %message"/>
        <Property name="bootstrap.servers">localhost:9092</Property>
    </Kafka>
  </Appenders>

This appender is synchronous by default and will block until the record has been acknowledged by the Kafka server, timeout for this can be set with the timeout.ms property (defaults to 30 seconds). Wrap with Async appender and/or set syncSend to false to log asynchronously.

This appender requires the Kafka client library. Note that you need to use a version of the Kafka client library matching the Kafka server used.

Note:Make sure to not let org.apache.kafka log to a Kafka appender on DEBUG level, since that will cause recursive logging:

<?xml version="1.0" encoding="UTF-8"?>
  ...
  <Loggers>
    <Root level="DEBUG">
      <AppenderRef ref="Kafka"/>
    </Root>
    <Logger name="org.apache.kafka" level="INFO" /> <!-- avoid recursive logging -->
  </Loggers>

MemoryMappedFileAppender

New since 2.1. Be aware that this is a new addition, and although it has been tested on several platforms, it does not have as much track record as the other file appenders.

The MemoryMappedFileAppender maps a part of the specified file into memory and writes log events to this memory, relying on the operating system's virtual memory manager to synchronize the changes to the storage device. The main benefit of using memory mapped files is I/O performance. Instead of making system calls to write to disk, this appender can simply change the program's local memory, which is orders of magnitude faster. Also, in most operating systems the memory region mapped actually is the kernel's page cache (file cache), meaning that no copies need to be created in user space. (TODO: performance tests that compare performance of this appender to RandomAccessFileAppender and FileAppender.)

There is some overhead with mapping a file region into memory, especially very large regions (half a gigabyte or more). The default region size is 32 MB, which should strike a reasonable balance between the frequency and the duration of remap operations. (TODO: performance test remapping various sizes.)

Similar to the FileAppender and the RandomAccessFileAppender, MemoryMappedFileAppender uses a MemoryMappedFileManager to actually perform the file I/O. While MemoryMappedFileAppender from different Configurations cannot be shared, the MemoryMappedFileManagers can be if the Manager is accessible. For example, two web applications in a servlet container can have their own configuration and safely write to the same file if Log4j is in a ClassLoader that is common to both of them.

MemoryMappedFileAppender Parameters
Parameter Name Type Description
append boolean When true - the default, records will be appended to the end of the file. When set to false, the file will be cleared before new records are written.
fileName String The name of the file to write to. If the file, or any of its parent directories, do not exist, they will be created.
filters Filter A Filter to determine if the event should be handled by this Appender. More than one Filter may be used by using a CompositeFilter.
immediateFlush boolean

When set to true, each write will be followed by a call to MappedByteBuffer.force(). This will guarantee the data is written to the storage device.

The default for this parameter is false. This means that the data is written to the storage device even if the Java process crashes, but there may be data loss if the operating system crashes.

Note that manually forcing a sync on every log event loses most of the performance benefits of using a memory mapped file.

Flushing after every write is only useful when using this appender with synchronous loggers. Asynchronous loggers and appenders will automatically flush at the end of a batch of events, even if immediateFlush is set to false. This also guarantees the data is written to disk but is more efficient.

regionLength int The length of the mapped region, defaults to 32 MB (32 * 1024 * 1024 bytes). This parameter must be a value between 256 and 1,073,741,824 (1 GB or 2^30); values outside this range will be adjusted to the closest valid value. Log4j will round the specified value up to the nearest power of two.
layout Layout The Layout to use to format the LogEvent. If no layout is supplied the default pattern layout of "%m%n" will be used.
name String The name of the Appender.
ignoreExceptions boolean The default is true, causing exceptions encountered while appending events to be internally logged and then ignored. When set to false exceptions will be propagated to the caller, instead. You must set this to false when wrapping this Appender in a FailoverAppender.

Here is a sample MemoryMappedFile configuration:

<?xml version="1.0" encoding="UTF-8"?>
<Configuration status="warn" name="MyApp" packages="">
  <Appenders>
    <MemoryMappedFile name="MyFile" fileName="logs/app.log">
      <PatternLayout>
        <Pattern>%d %p %c{1.} [%t] %m%n</Pattern>
      </PatternLayout>
    </MemoryMappedFile>
  </Appenders>
  <Loggers>
    <Root level="error">
      <AppenderRef ref="MyFile"/>
    </Root>
  </Loggers>
</Configuration>

NoSQLAppender

The NoSQLAppender writes log events to a NoSQL database using an internal lightweight provider interface. Provider implementations currently exist for MongoDB and Apache CouchDB, and writing a custom provider is quite simple.

NoSQLAppender Parameters
Parameter Name Type Description
name String Required. The name of the Appender.
ignoreExceptions boolean The default is true, causing exceptions encountered while appending events to be internally logged and then ignored. When set to false exceptions will be propagated to the caller, instead. You must set this to false when wrapping this Appender in a FailoverAppender.
filter Filter A Filter to determine if the event should be handled by this Appender. More than one Filter may be used by using a CompositeFilter.
bufferSize int If an integer greater than 0, this causes the appender to buffer log events and flush whenever the buffer reaches this size.
NoSqlProvider NoSQLProvider<C extends NoSQLConnection<W, T extends NoSQLObject<W>>> Required. The NoSQL provider that provides connections to the chosen NoSQL database.

You specify which NoSQL provider to use by specifying the appropriate configuration element within the <NoSql> element. The types currently supported are <MongoDb> and <CouchDb>. To create your own custom provider, read the JavaDoc for the NoSQLProvider, NoSQLConnection, and NoSQLObject classes and the documentation about creating Log4j plugins. We recommend you review the source code for the MongoDB and CouchDB providers as a guide for creating your own provider.

MongoDB Provider Parameters
Parameter Name Type Description
collectionName String Required. The name of the MongoDB collection to insert the events into.
writeConcernConstant Field By default, the MongoDB provider inserts records with the instructions com.mongodb.WriteConcern.ACKNOWLEDGED. Use this optional attribute to specify the name of a constant other than ACKNOWLEDGED.
writeConcernConstantClass Class If you specify writeConcernConstant, you can use this attribute to specify a class other than com.mongodb.WriteConcern to find the constant on (to create your own custom instructions).
factoryClassName Class To provide a connection to the MongoDB database, you can use this attribute and factoryMethodName to specify a class and static method to get the connection from. The method must return a com.mongodb.DB or a com.mongodb.MongoClient. If the DB is not authenticated, you must also specify a username and password. If you use the factory method for providing a connection, you must not specify the databaseName, server, or port attributes.
factoryMethodName Method See the documentation for attribute factoryClassName.
databaseName String If you do not specify a factoryClassName and factoryMethodName for providing a MongoDB connection, you must specify a MongoDB database name using this attribute. You must also specify a username and password. You can optionally also specify a server (defaults to localhost), and a port (defaults to the default MongoDB port).
server String See the documentation for attribute databaseName.
port int See the documentation for attribute databaseName.
username String See the documentation for attributes databaseName and factoryClassName.
password String See the documentation for attributes databaseName and factoryClassName.
CouchDB Provider Parameters
Parameter Name Type Description
factoryClassName Class To provide a connection to the CouchDB database, you can use this attribute and factoryMethodName to specify a class and static method to get the connection from. The method must return a org.lightcouch.CouchDbClient or a org.lightcouch.CouchDbProperties. If you use the factory method for providing a connection, you must not specify the databaseName, protocol, server, port, username, or password attributes.
factoryMethodName Method See the documentation for attribute factoryClassName.
databaseName String If you do not specify a factoryClassName and factoryMethodName for providing a CouchDB connection, you must specify a CouchDB database name using this attribute. You must also specify a username and password. You can optionally also specify a protocol (defaults to http), server (defaults to localhost), and a port (defaults to 80 for http and 443 for https).
protocol String Must either be "http" or "https." See the documentation for attribute databaseName.
server String See the documentation for attribute databaseName.
port int See the documentation for attribute databaseName.
username String See the documentation for attributes databaseName.
password String See the documentation for attributes databaseName.

Here are a few sample configurations for the NoSQLAppender:

<?xml version="1.0" encoding="UTF-8"?>
<Configuration status="error">
  <Appenders>
    <NoSql name="databaseAppender">
      <MongoDb databaseName="applicationDb" collectionName="applicationLog" server="mongo.example.org"
               username="loggingUser" password="abc123" />
    </NoSql>
  </Appenders>
  <Loggers>
    <Root level="warn">
      <AppenderRef ref="databaseAppender"/>
    </Root>
  </Loggers>
</Configuration>
<?xml version="1.0" encoding="UTF-8"?>
<Configuration status="error">
  <Appenders>
    <NoSql name="databaseAppender">
      <MongoDb collectionName="applicationLog" factoryClassName="org.example.db.ConnectionFactory"
               factoryMethodName="getNewMongoClient" />
    </NoSql>
  </Appenders>
  <Loggers>
    <Root level="warn">
      <AppenderRef ref="databaseAppender"/>
    </Root>
  </Loggers>
</Configuration>
<?xml version="1.0" encoding="UTF-8"?>
<Configuration status="error">
  <Appenders>
    <NoSql name="databaseAppender">
      <CouchDb databaseName="applicationDb" protocol="https" server="couch.example.org"
               username="loggingUser" password="abc123" />
    </NoSql>
  </Appenders>
  <Loggers>
    <Root level="warn">
      <AppenderRef ref="databaseAppender"/>
    </Root>
  </Loggers>
</Configuration>

The following example demonstrates how log events are persisted in NoSQL databases if represented in a JSON format:

{
    "level": "WARN",
    "loggerName": "com.example.application.MyClass",
    "message": "Something happened that you might want to know about.",
    "source": {
        "className": "com.example.application.MyClass",
        "methodName": "exampleMethod",
        "fileName": "MyClass.java",
        "lineNumber": 81
    },
    "marker": {
        "name": "SomeMarker",
        "parent" {
            "name": "SomeParentMarker"
        }
    },
    "threadName": "Thread-1",
    "millis": 1368844166761,
    "date": "2013-05-18T02:29:26.761Z",
    "thrown": {
        "type": "java.sql.SQLException",
        "message": "Could not insert record. Connection lost.",
        "stackTrace": [
                { "className": "org.example.sql.driver.PreparedStatement$1", "methodName": "responder", "fileName": "PreparedStatement.java", "lineNumber": 1049 },
                { "className": "org.example.sql.driver.PreparedStatement", "methodName": "executeUpdate", "fileName": "PreparedStatement.java", "lineNumber": 738 },
                { "className": "com.example.application.MyClass", "methodName": "exampleMethod", "fileName": "MyClass.java", "lineNumber": 81 },
                { "className": "com.example.application.MainClass", "methodName": "main", "fileName": "MainClass.java", "lineNumber": 52 }
        ],
        "cause": {
            "type": "java.io.IOException",
            "message": "Connection lost.",
            "stackTrace": [
                { "className": "java.nio.channels.SocketChannel", "methodName": "write", "fileName": null, "lineNumber": -1 },
                { "className": "org.example.sql.driver.PreparedStatement$1", "methodName": "responder", "fileName": "PreparedStatement.java", "lineNumber": 1032 },
                { "className": "org.example.sql.driver.PreparedStatement", "methodName": "executeUpdate", "fileName": "PreparedStatement.java", "lineNumber": 738 },
                { "className": "com.example.application.MyClass", "methodName": "exampleMethod", "fileName": "MyClass.java", "lineNumber": 81 },
                { "className": "com.example.application.MainClass", "methodName": "main", "fileName": "MainClass.java", "lineNumber": 52 }
            ]
        }
    },
    "contextMap": {
        "ID": "86c3a497-4e67-4eed-9d6a-2e5797324d7b",
        "username": "JohnDoe"
    },
    "contextStack": [
        "topItem",
        "anotherItem",
        "bottomItem"
    ]
}

OutputStreamAppender

The OutputStreamAppender provides the base for many of the other Appenders such as the File and Socket appenders that write the event to an Output Stream. It cannot be directly configured. Support for immediateFlush and buffering is provided by the OutputStreamAppender. The OutputStreamAppender uses an OutputStreamManager to handle the actual I/O, allowing the stream to be shared by Appenders in multiple configurations.

RandomAccessFileAppender

The RandomAccessFileAppender is similar to the standard FileAppender except it is always buffered (this cannot be switched off) and internally it uses a ByteBuffer + RandomAccessFile instead of a BufferedOutputStream. We saw a 20-200% performance improvement compared to FileAppender with "bufferedIO=true" in our measurements. Similar to the FileAppender, RandomAccessFileAppender uses a RandomAccessFileManager to actually perform the file I/O. While RandomAccessFileAppender from different Configurations cannot be shared, the RandomAccessFileManagers can be if the Manager is accessible. For example, two web applications in a servlet container can have their own configuration and safely write to the same file if Log4j is in a ClassLoader that is common to both of them.

RandomAccessFileAppender Parameters
Parameter Name Type Description
append boolean When true - the default, records will be appended to the end of the file. When set to false, the file will be cleared before new records are written.
fileName String The name of the file to write to. If the file, or any of its parent directories, do not exist, they will be created.
filters Filter A Filter to determine if the event should be handled by this Appender. More than one Filter may be used by using a CompositeFilter.
immediateFlush boolean

When set to true - the default, each write will be followed by a flush. This will guarantee the data is written to disk but could impact performance.

Flushing after every write is only useful when using this appender with synchronous loggers. Asynchronous loggers and appenders will automatically flush at the end of a batch of events, even if immediateFlush is set to false. This also guarantees the data is written to disk but is more efficient.

bufferSize int The buffer size, defaults to 262,144 bytes (256 * 1024).
layout Layout The Layout to use to format the LogEvent. If no layout is supplied the default pattern layout of "%m%n" will be used.
name String The name of the Appender.
ignoreExceptions boolean The default is true, causing exceptions encountered while appending events to be internally logged and then ignored. When set to false exceptions will be propagated to the caller, instead. You must set this to false when wrapping this Appender in a FailoverAppender.

Here is a sample RandomAccessFile configuration:

<?xml version="1.0" encoding="UTF-8"?>
<Configuration status="warn" name="MyApp" packages="">
  <Appenders>
    <RandomAccessFile name="MyFile" fileName="logs/app.log">
      <PatternLayout>
        <Pattern>%d %p %c{1.} [%t] %m%n</Pattern>
      </PatternLayout>
    </RandomAccessFile>
  </Appenders>
  <Loggers>
    <Root level="error">
      <AppenderRef ref="MyFile"/>
    </Root>
  </Loggers>
</Configuration>

RewriteAppender

The RewriteAppender allows the LogEvent to manipulated before it is processed by another Appender. This can be used to mask sensitive information such as passwords or to inject information into each event. The RewriteAppender must be configured with a RewritePolicy. The RewriteAppender should be configured after any Appenders it references to allow it to shut down properly.

RewriteAppender Parameters
Parameter Name Type Description
AppenderRef String The name of the Appenders to call after the LogEvent has been manipulated. Multiple AppenderRef elements can be configured.
filter Filter A Filter to determine if the event should be handled by this Appender. More than one Filter may be used by using a CompositeFilter.
name String The name of the Appender.
rewritePolicy RewritePolicy The RewritePolicy that will manipulate the LogEvent.
ignoreExceptions boolean The default is true, causing exceptions encountered while appending events to be internally logged and then ignored. When set to false exceptions will be propagated to the caller, instead. You must set this to false when wrapping this Appender in a FailoverAppender.

RewritePolicy

RewritePolicy is an interface that allows implementations to inspect and possibly modify LogEvents before they are passed to Appender. RewritePolicy declares a single method named rewrite that must be implemented. The method is passed the LogEvent and can return the same event or create a new one.

MapRewritePolicy

MapRewritePolicy will evaluate LogEvents that contain a MapMessage and will add or update elements of the Map.

Parameter Name Type Description
mode String "Add" or "Update"
keyValuePair KeyValuePair[] An array of keys and their values.

The following configuration shows a RewriteAppender configured to add a product key and its value to the MapMessage.:

<?xml version="1.0" encoding="UTF-8"?>
<Configuration status="warn" name="MyApp" packages="">
  <Appenders>
    <Console name="STDOUT" target="SYSTEM_OUT">
      <PatternLayout pattern="%m%n"/>
    </Console>
    <Rewrite name="rewrite">
      <AppenderRef ref="STDOUT"/>
      <MapRewritePolicy mode="Add">
        <KeyValuePair key="product" value="TestProduct"/>
      </MapRewritePolicy>
    </Rewrite>
  </Appenders>
  <Loggers>
    <Root level="error">
      <AppenderRef ref="Rewrite"/>
    </Root>
  </Loggers>
</Configuration>
PropertiesRewritePolicy

PropertiesRewritePolicy will add properties configured on the policy to the ThreadContext Map being logged. The properties will not be added to the actual ThreadContext Map. The property values may contain variables that will be evaluated when the configuration is processed as well as when the event is logged.

Parameter Name Type Description
properties Property[] One of more Property elements to define the keys and values to be added to the ThreadContext Map.

The following configuration shows a RewriteAppender configured to add a product key and its value to the MapMessage:

<?xml version="1.0" encoding="UTF-8"?>
<Configuration status="warn" name="MyApp" packages="">
  <Appenders>
    <Console name="STDOUT" target="SYSTEM_OUT">
      <PatternLayout pattern="%m%n"/>
    </Console>
    <Rewrite name="rewrite">
      <AppenderRef ref="STDOUT"/>
      <PropertiesRewritePolicy>
        <Property name="user">${sys:user.name}</Property>
        <Property name="env">${sys:environment}</Property>
      </PropertiesRewritePolicy>
    </Rewrite>
  </Appenders>
  <Loggers>
    <Root level="error">
      <AppenderRef ref="Rewrite"/>
    </Root>
  </Loggers>
</Configuration>
LoggerNameLevelRewritePolicy

You can use this policy to make loggers in third party code less chatty by changing event levels. The LoggerNameLevelRewritePolicy will rewrite log event levels for a given logger name prefix. You configure a LoggerNameLevelRewritePolicy with a logger name prefix and a pairs of levels, where a pair defines a source level and a target level.

Parameter Name Type Description
loggerName String A logger name used as a prefix to test each event's logger name.
LevelPair KeyValuePair[] An array of keys and their values, each key is a source level, each value a target level.

The following configuration shows a RewriteAppender configured to map level INFO to DEBUG and level WARN to INFO for all loggers that start with com.foo.bar.

<?xml version="1.0" encoding="UTF-8"?>
<Configuration status="warn" name="MyApp">
  <Appenders>
    <Console name="STDOUT" target="SYSTEM_OUT">
      <PatternLayout pattern="%m%n"/>
    </Console>
    <Rewrite name="rewrite">
      <AppenderRef ref="STDOUT"/>
      <LoggerNameLevelRewritePolicy loggerName="com.foo.bar">
        <KeyValuePair key="INFO" value="DEBUG"/>
        <KeyValuePair key="WARN" value="INFO"/>
      </LoggerNameLevelRewritePolicy>
    </Rewrite>
  </Appenders>
  <Loggers>
    <Root level="error">
      <AppenderRef ref="Rewrite"/>
    </Root>
  </Loggers>
</Configuration>

RollingFileAppender

The RollingFileAppender is an OutputStreamAppender that writes to the File named in the fileName parameter and rolls the file over according the TriggeringPolicy and the RolloverPolicy. The RollingFileAppender uses a RollingFileManager (which extends OutputStreamManager) to actually perform the file I/O and perform the rollover. While RolloverFileAppenders from different Configurations cannot be shared, the RollingFileManagers can be if the Manager is accessible. For example, two web applications in a servlet container can have their own configuration and safely write to the same file if Log4j is in a ClassLoader that is common to both of them.

A RollingFileAppender requires a TriggeringPolicy and a RolloverStrategy. The triggering policy determines if a rollover should be performed while the RolloverStrategy defines how the rollover should be done. If no RolloverStrategy is configured, RollingFileAppender will use the DefaultRolloverStrategy. Since log4j-2.5, a custom delete action can be configured in the DefaultRolloverStrategy to run at rollover. Since 2.8 if no file name is configured then DirectWriteRolloverStrategy will be used instead of DefaultRolloverStrategy.

File locking is not supported by the RollingFileAppender.

RollingFileAppender Parameters
Parameter Name Type Description
append boolean When true - the default, records will be appended to the end of the file. When set to false, the file will be cleared before new records are written.
bufferedIO boolean When true - the default, records will be written to a buffer and the data will be written to disk when the buffer is full or, if immediateFlush is set, when the record is written. File locking cannot be used with bufferedIO. Performance tests have shown that using buffered I/O significantly improves performance, even if immediateFlush is enabled.
bufferSize int When bufferedIO is true, this is the buffer size, the default is 8192 bytes.
createOnDemand boolean The appender creates the file on-demand. The appender only creates the file when a log event passes all filters and is routed to this appender. Defaults to false.
filter Filter A Filter to determine if the event should be handled by this Appender. More than one Filter may be used by using a CompositeFilter.
fileName String The name of the file to write to. If the file, or any of its parent directories, do not exist, they will be created.
filePattern String The pattern of the file name of the archived log file. The format of the pattern is dependent on the RolloverPolicy that is used. The DefaultRolloverPolicy will accept both a date/time pattern compatible with SimpleDateFormat and/or a %i which represents an integer counter. The pattern also supports interpolation at runtime so any of the Lookups (such as the DateLookup) can be included in the pattern.
immediateFlush boolean

When set to true - the default, each write will be followed by a flush. This will guarantee the data is written to disk but could impact performance.

Flushing after every write is only useful when using this appender with synchronous loggers. Asynchronous loggers and appenders will automatically flush at the end of a batch of events, even if immediateFlush is set to false. This also guarantees the data is written to disk but is more efficient.

layout Layout The Layout to use to format the LogEvent. If no layout is supplied the default pattern layout of "%m%n" will be used.
name String The name of the Appender.
policy TriggeringPolicy The policy to use to determine if a rollover should occur.
strategy RolloverStrategy The strategy to use to determine the name and location of the archive file.
ignoreExceptions boolean The default is true, causing exceptions encountered while appending events to be internally logged and then ignored. When set to false exceptions will be propagated to the caller, instead. You must set this to false when wrapping this Appender in a FailoverAppender.

Triggering Policies

Composite Triggering Policy

The CompositeTriggeringPolicy combines multiple triggering policies and returns true if any of the configured policies return true. The CompositeTriggeringPolicy is configured simply by wrapping other policies in a Policies element.

For example, the following XML fragment defines policies that rollover the log when the JVM starts, when the log size reaches twenty megabytes, and when the current date no longer matches the log’s start date.

<Policies>
  <OnStartupTriggeringPolicy />
  <SizeBasedTriggeringPolicy size="20 MB" />
  <TimeBasedTriggeringPolicy />
</Policies>
Cron Triggering Policy

The CronTriggeringPolicy triggers rollover based on a cron expression.

CronTriggeringPolicy Parameters
Parameter Name Type Description
schedule String The cron expression. The expression is the same as what is allowed in the Quartz scheduler. See CronExpression for a full description of the expression.
evaluateOnStartup boolean On startup the cron expression will be evaluated against the file's last modification timestamp. If the cron expression indicates a rollover should have occurred between that time and the current time the file will be immediately rolled over.
OnStartup Triggering Policy

The OnStartupTriggeringPolicy policy causes a rollover if the log file is older than the current JVM's start time and the minimum file size is met or exceeded.

OnStartupTriggeringPolicy Parameters
Parameter Name Type Description
minSize long The minimum size the file must have to roll over. A size of zero will cause a roll over no matter what the file size is. The default value is 1, which will prevent rolling over an empty file.

Google App Engine note:
When running in Google App Engine, the OnStartup policy causes a rollover if the log file is older than the time when Log4J initialized. (Google App Engine restricts access to certain classes so Log4J cannot determine JVM start time with java.lang.management.ManagementFactory.getRuntimeMXBean().getStartTime() and falls back to Log4J initialization time instead.)

SizeBased Triggering Policy

The SizeBasedTriggeringPolicy causes a rollover once the file has reached the specified size. The size can be specified in bytes, with the suffix KB, MB or GB, for example 20MB.

TimeBased Triggering Policy

The TimeBasedTriggeringPolicy causes a rollover once the date/time pattern no longer applies to the active file. This policy accepts an interval attribute which indicates how frequently the rollover should occur based on the time pattern and a modulate boolean attribute.

TimeBasedTriggeringPolicy Parameters
Parameter Name Type Description
interval integer How often a rollover should occur based on the most specific time unit in the date pattern. For example, with a date pattern with hours as the most specific item and and increment of 4 rollovers would occur every 4 hours. The default value is 1.
modulate boolean Indicates whether the interval should be adjusted to cause the next rollover to occur on the interval boundary. For example, if the item is hours, the current hour is 3 am and the interval is 4 then the first rollover will occur at 4 am and then next ones will occur at 8 am, noon, 4pm, etc.

Rollover Strategies

Default Rollover Strategy

The default rollover strategy accepts both a date/time pattern and an integer from the filePattern attribute specified on the RollingFileAppender itself. If the date/time pattern is present it will be replaced with the current date and time values. If the pattern contains an integer it will be incremented on each rollover. If the pattern contains both a date/time and integer in the pattern the integer will be incremented until the result of the date/time pattern changes. If the file pattern ends with ".gz", ".zip", ".bz2", ".deflate", ".pack200", or ".xz" the resulting archive will be compressed using the compression scheme that matches the suffix. The formats bzip2, Deflate, Pack200 and XZ require Apache Commons Compress. In addition, XZ requires XZ for Java. The pattern may also contain lookup references that can be resolved at runtime such as is shown in the example below.

The default rollover strategy supports three variations for incrementing the counter. The first is the "fixed window" strategy. To illustrate how it works, suppose that the min attribute is set to 1, the max attribute is set to 3, the file name is "foo.log", and the file name pattern is "foo-%i.log".

Number of rollovers Active output target Archived log files Description
0 foo.log - All logging is going to the initial file.
1 foo.log foo-1.log During the first rollover foo.log is renamed to foo-1.log. A new foo.log file is created and starts being written to.
2 foo.log foo-1.log, foo-2.log During the second rollover foo-1.log is renamed to foo-2.log and foo.log is renamed to foo-1.log. A new foo.log file is created and starts being written to.
3 foo.log foo-1.log, foo-2.log, foo-3.log During the third rollover foo-2.log is renamed to foo-3.log, foo-1.log is renamed to foo-2.log and foo.log is renamed to foo-1.log. A new foo.log file is created and starts being written to.
4 foo.log foo-1.log, foo-2.log, foo-3.log In the fourth and subsequent rollovers, foo-3.log is deleted, foo-2.log is renamed to foo-3.log, foo-1.log is renamed to foo-2.log and foo.log is renamed to foo-1.log. A new foo.log file is created and starts being written to.

By way of contrast, when the fileIndex attribute is set to "max" but all the other settings are the same the following actions will be performed.

Number of rollovers Active output target Archived log files Description
0 foo.log - All logging is going to the initial file.
1 foo.log foo-1.log During the first rollover foo.log is renamed to foo-1.log. A new foo.log file is created and starts being written to.
2 foo.log foo-1.log, foo-2.log During the second rollover foo.log is renamed to foo-2.log. A new foo.log file is created and starts being written to.
3 foo.log foo-1.log, foo-2.log, foo-3.log During the third rollover foo.log is renamed to foo-3.log. A new foo.log file is created and starts being written to.
4 foo.log foo-1.log, foo-2.log, foo-3.log In the fourth and subsequent rollovers, foo-1.log is deleted, foo-2.log is renamed to foo-1.log, foo-3.log is renamed to foo-2.log and foo.log is renamed to foo-3.log. A new foo.log file is created and starts being written to.

Finally, as of release 2.8, if the fileIndex attribute is set to "nomax" then the min and max values will be ignored and file numbering will increment by 1 and each rollover will have an incrementally higher value with no maximum number of files.

DefaultRolloverStrategy Parameters
Parameter Name Type Description
fileIndex String If set to "max" (the default), files with a higher index will be newer than files with a smaller index. If set to "min", file renaming and the counter will follow the Fixed Window strategy described above.
min integer The minimum value of the counter. The default value is 1.
max integer The maximum value of the counter. Once this values is reached older archives will be deleted on subsequent rollovers.
compressionLevel integer Sets the compression level, 0-9, where 0 = none, 1 = best speed, through 9 = best compression. Only implemented for ZIP files.
DirectWrite Rollover Strategy

The DirectWriteRolloverStrategy causes log events to be written directly to files represented by the file pattern. With this strategy file renames are not performed. If the size-based triggering policy causes multiple files to be written durring the specified time period they will be numbered starting at one and continually incremented until a time-based rollover occurs.

Warning: If the file pattern has a suffix indicating compression should take place the current file will not be compressed when the application is shut down. Furthermore, if the time changes such that the file pattern no longer matches the current file it will not be compressed at startup either.

DirectWriteRolloverStrategy Parameters
Parameter Name Type Description
maxFiles String The maximum number of files to allow in the time period matching the file pattern. If the number of files is exceeded the oldest file will be deleted. If specified, the value must be greater than 1. If the value is less than zero or omitted then the number of files will not be limited.
compressionLevel integer Sets the compression level, 0-9, where 0 = none, 1 = best speed, through 9 = best compression. Only implemented for ZIP files.

Below is a sample configuration that uses a RollingFileAppender with both the time and size based triggering policies, will create up to 7 archives on the same day (1-7) that are stored in a directory based on the current year and month, and will compress each archive using gzip:

<?xml version="1.0" encoding="UTF-8"?>
<Configuration status="warn" name="MyApp" packages="">
  <Appenders>
    <RollingFile name="RollingFile" fileName="logs/app.log"
                 filePattern="logs/$${date:yyyy-MM}/app-%d{MM-dd-yyyy}-%i.log.gz">
      <PatternLayout>
        <Pattern>%d %p %c{1.} [%t] %m%n</Pattern>
      </PatternLayout>
      <Policies>
        <TimeBasedTriggeringPolicy />
        <SizeBasedTriggeringPolicy size="250 MB"/>
      </Policies>
    </RollingFile>
  </Appenders>
  <Loggers>
    <Root level="error">
      <AppenderRef ref="RollingFile"/>
    </Root>
  </Loggers>
</Configuration>

This second example shows a rollover strategy that will keep up to 20 files before removing them.

<?xml version="1.0" encoding="UTF-8"?>
<Configuration status="warn" name="MyApp" packages="">
  <Appenders>
    <RollingFile name="RollingFile" fileName="logs/app.log"
                 filePattern="logs/$${date:yyyy-MM}/app-%d{MM-dd-yyyy}-%i.log.gz">
      <PatternLayout>
        <Pattern>%d %p %c{1.} [%t] %m%n</Pattern>
      </PatternLayout>
      <Policies>
        <TimeBasedTriggeringPolicy />
        <SizeBasedTriggeringPolicy size="250 MB"/>
      </Policies>
      <DefaultRolloverStrategy max="20"/>
    </RollingFile>
  </Appenders>
  <Loggers>
    <Root level="error">
      <AppenderRef ref="RollingFile"/>
    </Root>
  </Loggers>
</Configuration>

Below is a sample configuration that uses a RollingFileAppender with both the time and size based triggering policies, will create up to 7 archives on the same day (1-7) that are stored in a directory based on the current year and month, and will compress each archive using gzip and will roll every 6 hours when the hour is divisible by 6:

<?xml version="1.0" encoding="UTF-8"?>
<Configuration status="warn" name="MyApp" packages="">
  <Appenders>
    <RollingFile name="RollingFile" fileName="logs/app.log"
                 filePattern="logs/$${date:yyyy-MM}/app-%d{yyyy-MM-dd-HH}-%i.log.gz">
      <PatternLayout>
        <Pattern>%d %p %c{1.} [%t] %m%n</Pattern>
      </PatternLayout>
      <Policies>
        <TimeBasedTriggeringPolicy interval="6" modulate="true"/>
        <SizeBasedTriggeringPolicy size="250 MB"/>
      </Policies>
    </RollingFile>
  </Appenders>
  <Loggers>
    <Root level="error">
      <AppenderRef ref="RollingFile"/>
    </Root>
  </Loggers>
</Configuration>

This sample configuration uses a RollingFileAppender with both the cron and size based triggering policies, and writes directly to an unlimited number of archive files. The cron trigger causes a rollover every hour while the file size is limited to 250MB:

<?xml version="1.0" encoding="UTF-8"?>
<Configuration status="warn" name="MyApp" packages="">
  <Appenders>
    <RollingFile name="RollingFile" filePattern="logs/app-%d{yyyy-MM-dd-HH}-%i.log.gz">
      <PatternLayout>
        <Pattern>%d %p %c{1.} [%t] %m%n</Pattern>
      </PatternLayout>
      <Policies>
        <CronTriggeringPolicy schedule="0 0 * * * ?"/>
        <SizeBasedTriggeringPolicy size="250 MB"/>
      </Policies>
    </RollingFile>
  </Appenders>
  <Loggers>
    <Root level="error">
      <AppenderRef ref="RollingFile"/>
    </Root>
  </Loggers>
</Configuration>

This sample configuration is the same as the previous but limits the number of files saved each hour to 10:

<?xml version="1.0" encoding="UTF-8"?>
<Configuration status="warn" name="MyApp" packages="">
  <Appenders>
    <RollingFile name="RollingFile" filePattern="logs/app-%d{yyyy-MM-dd-HH}-%i.log.gz">
      <PatternLayout>
        <Pattern>%d %p %c{1.} [%t] %m%n</Pattern>
      </PatternLayout>
      <Policies>
        <CronTriggeringPolicy schedule="0 0 * * * ?"/>
        <SizeBasedTriggeringPolicy size="250 MB"/>
      </Policies>
      <DirectWriteRolloverStrategy maxFiles="10"/>
    </RollingFile>
  </Appenders>
  <Loggers>
    <Root level="error">
      <AppenderRef ref="RollingFile"/>
    </Root>
  </Loggers>
</Configuration>
Log Archive Retention Policy: Delete on Rollover

Log4j-2.5 introduces a Delete action that gives users more control over what files are deleted at rollover time than what was possible with the DefaultRolloverStrategy max attribute. The Delete action lets users configure one or more conditions that select the files to delete relative to a base directory.

Note that it is possible to delete any file, not just rolled over log files, so use this action with care! With the testMode parameter you can test your configuration without accidentally deleting the wrong files.

Delete Parameters
Parameter Name Type Description
basePath String Required. Base path from where to start scanning for files to delete.
maxDepth int The maximum number of levels of directories to visit. A value of 0 means that only the starting file (the base path itself) is visited, unless denied by the security manager. A value of Integer.MAX_VALUE indicates that all levels should be visited. The default is 1, meaning only the files in the specified base directory.
followLinks boolean Whether to follow symbolic links. Default is false.
testMode boolean If true, files are not deleted but instead a message is printed to the status logger at INFO level. Use this to do a dry run to test if the configuration works as expected. Default is false.
pathSorter PathSorter A plugin implementing the PathSorter interface to sort the files before selecting the files to delete. The default is to sort most recently modified files first.
pathConditions PathCondition[]

Required if no ScriptCondition is specified. One or more PathCondition elements.

If more than one condition is specified, they all need to accept a path before it is deleted. Conditions can be nested, in which case the inner condition(s) are evaluated only if the outer condition accepts the path. If conditions are not nested they may be evaluated in any order.

Conditions can also be combined with the logical operators AND, OR and NOT by using the IfAll, IfAny and IfNot composite conditions.

Users can create custom conditions or use the built-in conditions:

  • IfFileName - accepts files whose path (relative to the base path) matches a regular expression or a glob.
  • IfLastModified - accepts files that are as old as or older than the specified duration.
  • IfAccumulatedFileCount - accepts paths after some count threshold is exceeded during the file tree walk.
  • IfAccumulatedFileSize - accepts paths after the accumulated file size threshold is exceeded during the file tree walk.
  • IfAll - accepts a path if all nested conditions accept it (logical AND). Nested conditions may be evaluated in any order.
  • IfAny - accepts a path if one of the nested conditions accept it (logical OR). Nested conditions may be evaluated in any order.
  • IfNot - accepts a path if the nested condition does not accept it (logical NOT).
scriptCondition ScriptCondition

Required if no PathConditions are specified. A ScriptCondition element specifying a script.

The ScriptCondition should contain a Script, ScriptRef or ScriptFile element that specifies the logic to be executed. (See also the ScriptFilter documentation for more examples of configuring ScriptFiles and ScriptRefs.)

The script is passed a number of parameters, including a list of paths found under the base path (up to maxDepth) and must return a list with the paths to delete.

IfFileName Condition Parameters
Parameter Name Type Description
glob String Required if regex not specified. Matches the relative path (relative to the base path) using a limited pattern language that resembles regular expressions but with a simpler syntax.
regex String Required if glob not specified. Matches the relative path (relative to the base path) using a regular expression as defined by the Pattern class.
nestedConditions PathCondition[] An optional set of nested PathConditions. If any nested conditions exist they all need to accept the file before it is deleted. Nested conditions are only evaluated if the outer condition accepts a file (if the path name matches).
IfLastModified Condition Parameters
Parameter Name Type Description
age String Required. Specifies a duration. The condition accepts files that are as old or older than the specified duration.
nestedConditions PathCondition[] An optional set of nested PathConditions. If any nested conditions exist they all need to accept the file before it is deleted. Nested conditions are only evaluated if the outer condition accepts a file (if the file is old enough).
IfAccumulatedFileCount Condition Parameters
Parameter Name Type Description
exceeds int Required. The threshold count from which files will be deleted.
nestedConditions PathCondition[] An optional set of nested PathConditions. If any nested conditions exist they all need to accept the file before it is deleted. Nested conditions are only evaluated if the outer condition accepts a file (if the threshold count has been exceeded).
IfAccumulatedFileSize Condition Parameters
Parameter Name Type Description
exceeds String Required. The threshold accumulated file size from which files will be deleted. The size can be specified in bytes, with the suffix KB, MB or GB, for example 20MB.
nestedConditions PathCondition[] An optional set of nested PathConditions. If any nested conditions exist they all need to accept the file before it is deleted. Nested conditions are only evaluated if the outer condition accepts a file (if the threshold accumulated file size has been exceeded).

Below is a sample configuration that uses a RollingFileAppender with the cron triggering policy configured to trigger every day at midnight. Archives are stored in a directory based on the current year and month. All files under the base directory that match the "*/app-*.log.gz" glob and are 60 days old or older are deleted at rollover time.

<?xml version="1.0" encoding="UTF-8"?>
<Configuration status="warn" name="MyApp" packages="">
  <Properties>
    <Property name="baseDir">logs</Property>
  </Properties>
  <Appenders>
    <RollingFile name="RollingFile" fileName="${baseDir}/app.log"
          filePattern="${baseDir}/$${date:yyyy-MM}/app-%d{yyyy-MM-dd}.log.gz">
      <PatternLayout pattern="%d %p %c{1.} [%t] %m%n" />
      <CronTriggeringPolicy schedule="0 0 0 * * ?"/>
      <DefaultRolloverStrategy>
        <Delete basePath="${baseDir}" maxDepth="2">
          <IfFileName glob="*/app-*.log.gz" />
          <IfLastModified age="60d" />
        </Delete>
      </DefaultRolloverStrategy>
    </RollingFile>
  </Appenders>
  <Loggers>
    <Root level="error">
      <AppenderRef ref="RollingFile"/>
    </Root>
  </Loggers>
</Configuration>

Below is a sample configuration that uses a RollingFileAppender with both the time and size based triggering policies, will create up to 100 archives on the same day (1-100) that are stored in a directory based on the current year and month, and will compress each archive using gzip and will roll every hour. During every rollover, this configuration will delete files that match "*/app-*.log.gz" and are 30 days old or older, but keep the most recent 100 GB or the most recent 10 files, whichever comes first.

<?xml version="1.0" encoding="UTF-8"?>
<Configuration status="warn" name="MyApp" packages="">
  <Properties>
    <Property name="baseDir">logs</Property>
  </Properties>
  <Appenders>
    <RollingFile name="RollingFile" fileName="${baseDir}/app.log"
          filePattern="${baseDir}/$${date:yyyy-MM}/app-%d{yyyy-MM-dd-HH}-%i.log.gz">
      <PatternLayout pattern="%d %p %c{1.} [%t] %m%n" />
      <Policies>
        <TimeBasedTriggeringPolicy />
        <SizeBasedTriggeringPolicy size="250 MB"/>
      </Policies>
      <DefaultRolloverStrategy max="100">
        <!--
        Nested conditions: the inner condition is only evaluated on files
        for which the outer conditions are true.
        -->
        <Delete basePath="${baseDir}" maxDepth="2">
          <IfFileName glob="*/app-*.log.gz">
            <IfLastModified age="30d">
              <IfAny>
                <IfAccumulatedFileSize exceeds="100 GB" />
                <IfAccumulatedFileCount exceeds="10" />
              </IfAny>
            </IfLastModified>
          </IfFileName>
        </Delete>
      </DefaultRolloverStrategy>
    </RollingFile>
  </Appenders>
  <Loggers>
    <Root level="error">
      <AppenderRef ref="RollingFile"/>
    </Root>
  </Loggers>
</Configuration>
ScriptCondition Parameters
Parameter Name Type Description
script Script, ScriptFile or ScriptRef The Script element that specifies the logic to be executed. The script is passed a list of paths found under the base path and must return the paths to delete as a java.util.List<PathWithAttributes>. See also the ScriptFilter documentation for an example of how ScriptFiles and ScriptRefs can be configured.
Script Parameters
Parameter Name Type Description
basePath java.nio.file.Path The directory from where the Delete action started scanning for files to delete. Can be used to relativize the paths in the pathList.
pathList java.util.List<PathWithAttributes> The list of paths found under the base path up to the specified max depth, sorted most recently modified files first. The script is free to modify and return this list.
statusLogger StatusLogger The StatusLogger that can be used to log internal events during script execution.
configuration Configuration The Configuration that owns this ScriptCondition.
substitutor StrSubstitutor The StrSubstitutor used to replace lookup variables.
? String Any properties declared in the configuration.

Below is a sample configuration that uses a RollingFileAppender with the cron triggering policy configured to trigger every day at midnight. Archives are stored in a directory based on the current year and month. The script returns a list of rolled over files under the base directory dated Friday the 13th. The Delete action will delete all files returned by the script.

<?xml version="1.0" encoding="UTF-8"?>
<Configuration status="trace" name="MyApp" packages="">
  <Properties>
    <Property name="baseDir">logs</Property>
  </Properties>
  <Appenders>
    <RollingFile name="RollingFile" fileName="${baseDir}/app.log"
          filePattern="${baseDir}/$${date:yyyy-MM}/app-%d{yyyyMMdd}.log.gz">
      <PatternLayout pattern="%d %p %c{1.} [%t] %m%n" />
      <CronTriggeringPolicy schedule="0 0 0 * * ?"/>
      <DefaultRolloverStrategy>
        <Delete basePath="${baseDir}" maxDepth="2">
          <ScriptCondition>
            <Script name="superstitious" language="groovy"><![CDATA[
                import java.nio.file.*;

                def result = [];
                def pattern = ~/\d*\/app-(\d*)\.log\.gz/;

                pathList.each { pathWithAttributes ->
                  def relative = basePath.relativize pathWithAttributes.path
                  statusLogger.trace 'SCRIPT: relative path=' + relative + " (base=$basePath)";

                  // remove files dated Friday the 13th

                  def matcher = pattern.matcher(relative.toString());
                  if (matcher.find()) {
                    def dateString = matcher.group(1);
                    def calendar = Date.parse("yyyyMMdd", dateString).toCalendar();
                    def friday13th = calendar.get(Calendar.DAY_OF_MONTH) == 13 \
                                  && calendar.get(Calendar.DAY_OF_WEEK) == Calendar.FRIDAY;
                    if (friday13th) {
                      result.add pathWithAttributes;
                      statusLogger.trace 'SCRIPT: deleting path ' + pathWithAttributes;
                    }
                  }
                }
                statusLogger.trace 'SCRIPT: returning ' + result;
                result;
              ]] >
            </Script>
          </ScriptCondition>
        </Delete>
      </DefaultRolloverStrategy>
    </RollingFile>
  </Appenders>
  <Loggers>
    <Root level="error">
      <AppenderRef ref="RollingFile"/>
    </Root>
  </Loggers>
</Configuration>

RollingRandomAccessFileAppender

The RollingRandomAccessFileAppender is similar to the standard RollingFileAppender except it is always buffered (this cannot be switched off) and internally it uses a ByteBuffer + RandomAccessFile instead of a BufferedOutputStream. We saw a 20-200% performance improvement compared to RollingFileAppender with "bufferedIO=true" in our measurements. The RollingRandomAccessFileAppender writes to the File named in the fileName parameter and rolls the file over according the TriggeringPolicy and the RolloverPolicy. Similar to the RollingFileAppender, RollingRandomAccessFileAppender uses a RollingRandomAccessFileManager to actually perform the file I/O and perform the rollover. While RollingRandomAccessFileAppender from different Configurations cannot be shared, the RollingRandomAccessFileManagers can be if the Manager is accessible. For example, two web applications in a servlet container can have their own configuration and safely write to the same file if Log4j is in a ClassLoader that is common to both of them.

A RollingRandomAccessFileAppender requires a TriggeringPolicy and a RolloverStrategy. The triggering policy determines if a rollover should be performed while the RolloverStrategy defines how the rollover should be done. If no RolloverStrategy is configured, RollingRandomAccessFileAppender will use the DefaultRolloverStrategy. Since log4j-2.5, a custom delete action can be configured in the DefaultRolloverStrategy to run at rollover.

File locking is not supported by the RollingRandomAccessFileAppender.

RollingRandomAccessFileAppender Parameters
Parameter Name Type Description
append boolean When true - the default, records will be appended to the end of the file. When set to false, the file will be cleared before new records are written.
filter Filter A Filter to determine if the event should be handled by this Appender. More than one Filter may be used by using a CompositeFilter.
fileName String The name of the file to write to. If the file, or any of its parent directories, do not exist, they will be created.
filePattern String The pattern of the file name of the archived log file. The format of the pattern should is dependent on the RolloverPolicy that is used. The DefaultRolloverPolicy will accept both a date/time pattern compatible with SimpleDateFormat and/or a %i which represents an integer counter. The pattern also supports interpolation at runtime so any of the Lookups (such as the DateLookup can be included in the pattern.
immediateFlush boolean

When set to true - the default, each write will be followed by a flush. This will guarantee the data is written to disk but could impact performance.

Flushing after every write is only useful when using this appender with synchronous loggers. Asynchronous loggers and appenders will automatically flush at the end of a batch of events, even if immediateFlush is set to false. This also guarantees the data is written to disk but is more efficient.

bufferSize int The buffer size, defaults to 262,144 bytes (256 * 1024).
layout Layout The Layout to use to format the LogEvent. If no layout is supplied the default pattern layout of "%m%n" will be used.
name String The name of the Appender.
policy TriggeringPolicy The policy to use to determine if a rollover should occur.
strategy RolloverStrategy The strategy to use to determine the name and location of the archive file.
ignoreExceptions boolean The default is true, causing exceptions encountered while appending events to be internally logged and then ignored. When set to false exceptions will be propagated to the caller, instead. You must set this to false when wrapping this Appender in a FailoverAppender.

Triggering Policies

See RollingFileAppender Triggering Policies.

Rollover Strategies

See RollingFileAppender Rollover Strategies.

Below is a sample configuration that uses a RollingRandomAccessFileAppender with both the time and size based triggering policies, will create up to 7 archives on the same day (1-7) that are stored in a directory based on the current year and month, and will compress each archive using gzip:

<?xml version="1.0" encoding="UTF-8"?>
<Configuration status="warn" name="MyApp" packages="">
  <Appenders>
    <RollingRandomAccessFile name="RollingRandomAccessFile" fileName="logs/app.log"
                 filePattern="logs/$${date:yyyy-MM}/app-%d{MM-dd-yyyy}-%i.log.gz">
      <PatternLayout>
        <Pattern>%d %p %c{1.} [%t] %m%n</Pattern>
      </PatternLayout>
      <Policies>
        <TimeBasedTriggeringPolicy />
        <SizeBasedTriggeringPolicy size="250 MB"/>
      </Policies>
    </RollingRandomAccessFile>
  </Appenders>
  <Loggers>
    <Root level="error">
      <AppenderRef ref="RollingRandomAccessFile"/>
    </Root>
  </Loggers>
</Configuration>

This second example shows a rollover strategy that will keep up to 20 files before removing them.

<?xml version="1.0" encoding="UTF-8"?>
<Configuration status="warn" name="MyApp" packages="">
  <Appenders>
    <RollingRandomAccessFile name="RollingRandomAccessFile" fileName="logs/app.log"
                 filePattern="logs/$${date:yyyy-MM}/app-%d{MM-dd-yyyy}-%i.log.gz">
      <PatternLayout>
        <Pattern>%d %p %c{1.} [%t] %m%n</Pattern>
      </PatternLayout>
      <Policies>
        <TimeBasedTriggeringPolicy />
        <SizeBasedTriggeringPolicy size="250 MB"/>
      </Policies>
      <DefaultRolloverStrategy max="20"/>
    </RollingRandomAccessFile>
  </Appenders>
  <Loggers>
    <Root level="error">
      <AppenderRef ref="RollingRandomAccessFile"/>
    </Root>
  </Loggers>
</Configuration>

Below is a sample configuration that uses a RollingRandomAccessFileAppender with both the time and size based triggering policies, will create up to 7 archives on the same day (1-7) that are stored in a directory based on the current year and month, and will compress each archive using gzip and will roll every 6 hours when the hour is divisible by 6:

<?xml version="1.0" encoding="UTF-8"?>
<Configuration status="warn" name="MyApp" packages="">
  <Appenders>
    <RollingRandomAccessFile name="RollingRandomAccessFile" fileName="logs/app.log"
                 filePattern="logs/$${date:yyyy-MM}/app-%d{yyyy-MM-dd-HH}-%i.log.gz">
      <PatternLayout>
        <Pattern>%d %p %c{1.} [%t] %m%n</Pattern>
      </PatternLayout>
      <Policies>
        <TimeBasedTriggeringPolicy interval="6" modulate="true"/>
        <SizeBasedTriggeringPolicy size="250 MB"/>
      </Policies>
    </RollingRandomAccessFile>
  </Appenders>
  <Loggers>
    <Root level="error">
      <AppenderRef ref="RollingRandomAccessFile"/>
    </Root>
  </Loggers>
</Configuration>

RoutingAppender

The RoutingAppender evaluates LogEvents and then routes them to a subordinate Appender. The target Appender may be an appender previously configured and may be referenced by its name or the Appender can be dynamically created as needed. The RoutingAppender should be configured after any Appenders it references to allow it to shut down properly.

You can also configure a RoutingAppender with scripts: you can run a script when the appender starts and when a route is chosen for an log event.

RoutingAppender Parameters
Parameter Name Type Description
Filter Filter A Filter to determine if the event should be handled by this Appender. More than one Filter may be used by using a CompositeFilter.
name String The name of the Appender.
RewritePolicy RewritePolicy The RewritePolicy that will manipulate the LogEvent.
Routes Routes Contains one or more Route declarations to identify the criteria for choosing Appenders.
Script Script

This Script runs when Log4j starts the RoutingAppender and returns a String Route key to determine the default Route.

This script is passed the following variables:

RoutingAppender Script Parameters
Parameter Name Type Description
configuration Configuration The active Configuration.
staticVariables Map A Map shared between all script invocations for this appender instance. This is the same map passed to the Routes Script.
ignoreExceptions boolean The default is true, causing exceptions encountered while appending events to be internally logged and then ignored. When set to false exceptions will be propagated to the caller, instead. You must set this to false when wrapping this Appender in a FailoverAppender.

In this example, the script causes the "ServiceWindows" route to be the default route on Windows and "ServiceOther" on all other operating systems. Note that the List Appender is one of our test appenders, any appender can be used, it is only used as a shorthand.

<?xml version="1.0" encoding="UTF-8"?>
<Configuration status="WARN" name="RoutingTest">
  <Appenders>
    <Routing name="Routing">
      <Script name="RoutingInit" language="JavaScript"><![CDATA[
        importPackage(java.lang);
        System.getProperty("os.name").search("Windows") > -1 ? "ServiceWindows" : "ServiceOther";]]>
      </Script>
      <Routes>
        <Route key="ServiceOther">
          <List name="List1" />
        </Route>
        <Route key="ServiceWindows">
          <List name="List2" />
        </Route>
      </Routes>
    </Routing>
  </Appenders>
  <Loggers>
    <Root level="error">
      <AppenderRef ref="Routing" />
    </Root>
  </Loggers>
</Configuration>

Routes

The Routes element accepts a single attribute named "pattern". The pattern is evaluated against all the registered Lookups and the result is used to select a Route. Each Route may be configured with a key. If the key matches the result of evaluating the pattern then that Route will be selected. If no key is specified on a Route then that Route is the default. Only one Route can be configured as the default.

The Routes element may contain a Script child element. If specified, the Script is run for each log event and returns the String Route key to use.

You must specify either the pattern attribute or the Script element, but not both.

Each Route must reference an Appender. If the Route contains a ref attribute then the Route will reference an Appender that was defined in the configuration. If the Route contains an Appender definition then an Appender will be created within the context of the RoutingAppender and will be reused each time a matching Appender name is referenced through a Route.

This script is passed the following variables:

RoutingAppender Routes Script Parameters
Parameter Name Type Description
configuration Configuration The active Configuration.
staticVariables Map A Map shared between all script invocations for this appender instance. This is the same map passed to the Routes Script.
logEvent LogEvent The log event.

In this example, the script runs for each log event and picks a route based on the presence of a Marker named "AUDIT".

<?xml version="1.0" encoding="UTF-8"?>
<Configuration status="WARN" name="RoutingTest">
  <Appenders>
    <Console name="STDOUT" target="SYSTEM_OUT" />
    <Flume name="AuditLogger" compress="true">
      <Agent host="192.168.10.101" port="8800"/>
      <Agent host="192.168.10.102" port="8800"/>
      <RFC5424Layout enterpriseNumber="18060" includeMDC="true" appName="MyApp"/>
    </Flume>
    <Routing name="Routing">
      <Routes>
        <Script name="RoutingInit" language="JavaScript"><![CDATA[
          if (logEvent.getMarker() != null && logEvent.getMarker().isInstanceOf("AUDIT")) {
                return "AUDIT";
            } else if (logEvent.getContextMap().containsKey("UserId")) {
                return logEvent.getContextMap().get("UserId");
            }
            return "STDOUT";]]>
        </Script>
        <Route>
          <RollingFile
              name="Rolling-${mdc:UserId}"
              fileName="${mdc:UserId}.log"
              filePattern="${mdc:UserId}.%i.log.gz">
            <PatternLayout>
              <pattern>%d %p %c{1.} [%t] %m%n</pattern>
            </PatternLayout>
            <SizeBasedTriggeringPolicy size="500" />
          </RollingFile>
        </Route>
        <Route ref="AuditLogger" key="AUDIT"/>
        <Route ref="STDOUT" key="STDOUT"/>
      </Routes>
      <IdlePurgePolicy timeToLive="15" timeUnit="minutes"/>
    </Routing>
  </Appenders>
  <Loggers>
    <Root level="error">
      <AppenderRef ref="Routing" />
    </Root>
  </Loggers>
</Configuration>

Purge Policy

The RoutingAppender can be configured with a PurgePolicy whose purpose is to stop and remove dormant Appenders that have been dynamically created by the RoutingAppender. Log4j currently provides the IdlePurgePolicy as the only PurgePolicy available for cleaning up the Appenders. The IdlePurgePolicy accepts 2 attributes; timeToLive, which is the number of timeUnits the Appender should survive without having any events sent to it, and timeUnit, the String representation of java.util.concurrent.TimeUnit which is used with the timeToLive attribute.

Below is a sample configuration that uses a RoutingAppender to route all Audit events to a FlumeAppender and all other events will be routed to a RollingFileAppender that captures only the specific event type. Note that the AuditAppender was predefined while the RollingFileAppenders are created as needed.

<?xml version="1.0" encoding="UTF-8"?>
<Configuration status="warn" name="MyApp" packages="">
  <Appenders>
    <Flume name="AuditLogger" compress="true">
      <Agent host="192.168.10.101" port="8800"/>
      <Agent host="192.168.10.102" port="8800"/>
      <RFC5424Layout enterpriseNumber="18060" includeMDC="true" appName="MyApp"/>
    </Flume>
    <Routing name="Routing">
      <Routes pattern="$${sd:type}">
        <Route>
          <RollingFile name="Rolling-${sd:type}" fileName="${sd:type}.log"
                       filePattern="${sd:type}.%i.log.gz">
            <PatternLayout>
              <pattern>%d %p %c{1.} [%t] %m%n</pattern>
            </PatternLayout>
            <SizeBasedTriggeringPolicy size="500" />
          </RollingFile>
        </Route>
        <Route ref="AuditLogger" key="Audit"/>
      </Routes>
      <IdlePurgePolicy timeToLive="15" timeUnit="minutes"/>
    </Routing>
  </Appenders>
  <Loggers>
    <Root level="error">
      <AppenderRef ref="Routing"/>
    </Root>
  </Loggers>
</Configuration>

SMTPAppender

Sends an e-mail when a specific logging event occurs, typically on errors or fatal errors.

The number of logging events delivered in this e-mail depend on the value of BufferSize option. The SMTPAppender keeps only the last BufferSize logging events in its cyclic buffer. This keeps memory requirements at a reasonable level while still delivering useful application context. All events in the buffer are included in the email. The buffer will contain the most recent events of level TRACE to WARN preceding the event that triggered the email.

The default behavior is to trigger sending an email whenever an ERROR or higher severity event is logged and to format it as HTML. The circumstances on when the email is sent can be controlled by setting one or more filters on the Appender. As with other Appenders, the formatting can be controlled by specifying a Layout for the Appender.

SMTPAppender Parameters
Parameter Name Type Description
bcc String The comma-separated list of BCC email addresses.
cc String The comma-separated list of CC email addresses.
bufferSize integer The maximum number of log events to be buffered for inclusion in the message. Defaults to 512.
filter Filter A Filter to determine if the event should be handled by this Appender. More than one Filter may be used by using a CompositeFilter.
from String The email address of the sender.
layout Layout The Layout to use to format the LogEvent. If no layout is supplied HTML layout will be used.
name String The name of the Appender.
replyTo String The comma-separated list of reply-to email addresses.
smtpDebug boolean When set to true enables session debugging on STDOUT. Defaults to false.
smtpHost String The SMTP hostname to send to. This parameter is required.
smtpPassword String The password required to authenticate against the SMTP server.
smtpPort integer The SMTP port to send to.
smtpProtocol String The SMTP transport protocol (such as "smtps", defaults to "smtp").
smtpUsername String The username required to authenticate against the SMTP server.
ignoreExceptions boolean The default is true, causing exceptions encountered while appending events to be internally logged and then ignored. When set to false exceptions will be propagated to the caller, instead. You must set this to false when wrapping this Appender in a FailoverAppender.
to String The comma-separated list of recipient email addresses.
<?xml version="1.0" encoding="UTF-8"?>
<Configuration status="warn" name="MyApp" packages="">
  <Appenders>
    <SMTP name="Mail" subject="Error Log" to="errors@logging.apache.org" from="test@logging.apache.org"
          smtpHost="localhost" smtpPort="25" bufferSize="50">
    </SMTP>
  </Appenders>
  <Loggers>
    <Root level="error">
      <AppenderRef ref="Mail"/>
    </Root>
  </Loggers>
</Configuration>

ScriptAppenderSelector

When the configuration is built, the ScriptAppenderSelector appender calls a Script to compute an appender name. Log4j then creates one of the appender named listed under AppenderSet using the name of the ScriptAppenderSelector. After configuration, Log4j ignores the ScriptAppenderSelector. Log4j only builds the one selected appender from the configuration tree, and ignores other AppenderSet child nodes.

In the following example, the script returns the name "List2". The appender name is recorded under the name of the ScriptAppenderSelector, not the name of the selected appender, in this example, "SelectIt".

<Configuration status="WARN" name="ScriptAppenderSelectorExample">
  <Appenders>
    <ScriptAppenderSelector name="SelectIt">
      <Script language="JavaScript"><![CDATA[
        importPackage(java.lang);
        System.getProperty("os.name").search("Windows") > -1 ? "MyCustomWindowsAppender" : "MySyslogAppender";]]>
      </Script>
      <AppenderSet>
        <MyCustomWindowsAppender name="MyAppender" ... />
        <SyslogAppender name="MySyslog" ... />
      </AppenderSet>
    </ScriptAppenderSelector>
  </Appenders>
  <Loggers>
    <Root level="error">
      <AppenderRef ref="SelectIt" />
    </Root>
  </Loggers>
</Configuration>

SocketAppender

The SocketAppender is an OutputStreamAppender that writes its output to a remote destination specified by a host and port. The data can be sent over either TCP or UDP and can be sent in any format. The default format is to send a Serialized LogEvent. Log4j 2 contains a SocketServer which is capable of receiving serialized LogEvents and routing them through the logging system on the server. You can optionally secure communication with SSL.

SocketAppender Parameters
Parameter Name Type Description
name String The name of the Appender.
host String The name or address of the system that is listening for log events. This parameter is required.
port integer The port on the host that is listening for log events. This parameter must be specified.
protocol String "TCP" (default), "SSL" or "UDP".
SSL SslConfiguration Contains the configuration for the KeyStore and TrustStore.
filter Filter A Filter to determine if the event should be handled by this Appender. More than one Filter may be used by using a CompositeFilter.
immediateFail boolean When set to true, log events will not wait to try to reconnect and will fail immediately if the socket is not available.
immediateFlush boolean When set to true - the default, each write will be followed by a flush. This will guarantee the data is written to disk but could impact performance.
bufferedIO boolean When true - the default, events are written to a buffer and the data will be written to the socket when the buffer is full or, if immediateFlush is set, when the record is written.
bufferSize int When bufferedIO is true, this is the buffer size, the default is 8192 bytes.
layout Layout The Layout to use to format the LogEvent. The default is SerializedLayout.
reconnectionDelayMillis integer If set to a value greater than 0, after an error the SocketManager will attempt to reconnect to the server after waiting the specified number of milliseconds. If the reconnect fails then an exception will be thrown (which can be caught by the application if ignoreExceptions is set to false).
connectTimeoutMillis integer The connect timeout in milliseconds. The default is 0 (infinite timeout, like Socket.connect() methods).
ignoreExceptions boolean The default is true, causing exceptions encountered while appending events to be internally logged and then ignored. When set to false exceptions will be propagated to the caller, instead. You must set this to false when wrapping this Appender in a FailoverAppender.

This is an unsecured TCP configuration:

<?xml version="1.0" encoding="UTF-8"?>
<Configuration status="warn" name="MyApp" packages="">
  <Appenders>
    <Socket name="socket" host="localhost" port="9500">
      <SerializedLayout />
    </Socket>
  </Appenders>
  <Loggers>
    <Root level="error">
      <AppenderRef ref="socket"/>
    </Root>
  </Loggers>
</Configuration>

This is a secured SSL configuration:

<?xml version="1.0" encoding="UTF-8"?>
<Configuration status="warn" name="MyApp" packages="">
  <Appenders>
    <Socket name="socket" host="localhost" port="9500">
      <SerializedLayout />
      <SSL>
        <KeyStore location="log4j2-keystore.jks" password="changeme"/>
        <TrustStore location="truststore.jks" password="changeme"/>
      </SSL>
    </Socket>
  </Appenders>
  <Loggers>
    <Root level="error">
      <AppenderRef ref="socket"/>
    </Root>
  </Loggers>
</Configuration>

SyslogAppender

The SyslogAppender is a SocketAppender that writes its output to a remote destination specified by a host and port in a format that conforms with either the BSD Syslog format or the RFC 5424 format. The data can be sent over either TCP or UDP.

SyslogAppender Parameters
Parameter Name Type Description
advertise boolean Indicates whether the appender should be advertised.
appName String The value to use as the APP-NAME in the RFC 5424 syslog record.
charset String The character set to use when converting the syslog String to a byte array. The String must be a valid Charset. If not specified, the default system Charset will be used.
connectTimeoutMillis integer The connect timeout in milliseconds. The default is 0 (infinite timeout, like Socket.connect() methods).
enterpriseNumber integer The IANA enterprise number as described in RFC 5424
filter Filter A Filter to determine if the event should be handled by this Appender. More than one Filter may be used by using a CompositeFilter.
facility String The facility is used to try to classify the message. The facility option must be set to one of "KERN", "USER", "MAIL", "DAEMON", "AUTH", "SYSLOG", "LPR", "NEWS", "UUCP", "CRON", "AUTHPRIV", "FTP", "NTP", "AUDIT", "ALERT", "CLOCK", "LOCAL0", "LOCAL1", "LOCAL2", "LOCAL3", "LOCAL4", "LOCAL5", "LOCAL6", or "LOCAL7". These values may be specified as upper or lower case characters.
format String If set to "RFC5424" the data will be formatted in accordance with RFC 5424. Otherwise, it will be formatted as a BSD Syslog record. Note that although BSD Syslog records are required to be 1024 bytes or shorter the SyslogLayout does not truncate them. The RFC5424Layout also does not truncate records since the receiver must accept records of up to 2048 bytes and may accept records that are longer.
host String The name or address of the system that is listening for log events. This parameter is required.
id String The default structured data id to use when formatting according to RFC 5424. If the LogEvent contains a StructuredDataMessage the id from the Message will be used instead of this value.
ignoreExceptions boolean The default is true, causing exceptions encountered while appending events to be internally logged and then ignored. When set to false exceptions will be propagated to the caller, instead. You must set this to false when wrapping this Appender in a FailoverAppender.
immediateFail boolean When set to true, log events will not wait to try to reconnect and will fail immediately if the socket is not available.
immediateFlush boolean When set to true - the default, each write will be followed by a flush. This will guarantee the data is written to disk but could impact performance.
includeMDC boolean Indicates whether data from the ThreadContextMap will be included in the RFC 5424 Syslog record. Defaults to true.
Layout Layout A custom layout which overrides the format setting.
loggerFields List of KeyValuePairs Allows arbitrary PatternLayout patterns to be included as specified ThreadContext fields; no default specified. To use, include a >LoggerFields< nested element, containing one or more >KeyValuePair< elements. Each >KeyValuePair< must have a key attribute, which specifies the key name which will be used to identify the field within the MDC Structured Data element, and a value attribute, which specifies the PatternLayout pattern to use as the value.
mdcExcludes String A comma separated list of mdc keys that should be excluded from the LogEvent. This is mutually exclusive with the mdcIncludes attribute. This attribute only applies to RFC 5424 syslog records.
mdcIncludes String A comma separated list of mdc keys that should be included in the FlumeEvent. Any keys in the MDC not found in the list will be excluded. This option is mutually exclusive with the mdcExcludes attribute. This attribute only applies to RFC 5424 syslog records.
mdcRequired String A comma separated list of mdc keys that must be present in the MDC. If a key is not present a LoggingException will be thrown. This attribute only applies to RFC 5424 syslog records.
mdcPrefix String A string that should be prepended to each MDC key in order to distinguish it from event attributes. The default string is "mdc:". This attribute only applies to RFC 5424 syslog records.
messageId String The default value to be used in the MSGID field of RFC 5424 syslog records.
name String The name of the Appender.
newLine boolean If true, a newline will be appended to the end of the syslog record. The default is false.
port integer The port on the host that is listening for log events. This parameter must be specified.
protocol String "TCP" or "UDP". This parameter is required.
SSL SslConfiguration Contains the configuration for the KeyStore and TrustStore.
reconnectionDelayMillis integer If set to a value greater than 0, after an error the SocketManager will attempt to reconnect to the server after waiting the specified number of milliseconds. If the reconnect fails then an exception will be thrown (which can be caught by the application if ignoreExceptions is set to false).

A sample syslogAppender configuration that is configured with two SyslogAppenders, one using the BSD format and one using RFC 5424.

<?xml version="1.0" encoding="UTF-8"?>
<Configuration status="warn" name="MyApp" packages="">
  <Appenders>
    <Syslog name="bsd" host="localhost" port="514" protocol="TCP"/>
    <Syslog name="RFC5424" format="RFC5424" host="localhost" port="8514"
            protocol="TCP" appName="MyApp" includeMDC="true"
            facility="LOCAL0" enterpriseNumber="18060" newLine="true"
            messageId="Audit" id="App"/>
  </Appenders>
  <Loggers>
    <Logger name="com.mycorp" level="error">
      <AppenderRef ref="RFC5424"/>
    </Logger>
    <Root level="error">
      <AppenderRef ref="bsd"/>
    </Root>
  </Loggers>
</Configuration>

For SSL this appender writes its output to a remote destination specified by a host and port over SSL in a format that conforms with either the BSD Syslog format or the RFC 5424 format.

<?xml version="1.0" encoding="UTF-8"?>
<Configuration status="warn" name="MyApp" packages="">
  <Appenders>
    <TLSSyslog name="bsd" host="localhost" port="6514">
      <SSL>
        <KeyStore location="log4j2-keystore.jks" password="changeme"/>
        <TrustStore location="truststore.jks" password="changeme"/>
      </SSL>
    </TLSSyslog>
  </Appenders>
  <Loggers>
    <Root level="error">
      <AppenderRef ref="bsd"/>
    </Root>
  </Loggers>
</Configuration>

ZeroMQ/JeroMQ Appender

The ZeroMQ appender uses the JeroMQ library to send log events to one or more ZeroMQ endpoints.

This is a simple JeroMQ configuration:

<?xml version="1.0" encoding="UTF-8"?>
<Configuration name="JeroMQAppenderTest" status="TRACE">
  <Appenders>
    <JeroMQ name="JeroMQAppender">
      <Property name="endpoint">tcp://*:5556</Property>
      <Property name="endpoint">ipc://info-topic</Property>
    </JeroMQ>
  </Appenders>
  <Loggers>
    <Root level="info">
      <AppenderRef ref="JeroMQAppender"/>
    </Root>
  </Loggers>
</Configuration>

The table below describes all options. Please consult the JeroMQ and ZeroMQ documentation for details.

JeroMQ Parameters
Parameter Name Type Description
name String The name of the Appender. Required.
Layout layout The Layout to use to format the LogEvent. If no layout is supplied the default pattern layout of "%m%n" will be used.
Filters Filter The Filter(s) of the Appender.
Properties Property[] One or more Property elements, named endpoint.
ignoreExceptions boolean If true, exceptions will be logged and suppressed. If false errors will be logged and then passed to the application.
affinity long The ZMQ_AFFINITY option. Defaults to 0.
backlog long The ZMQ_BACKLOG option. Defaults to 100.
delayAttachOnConnect boolean The ZMQ_DELAY_ATTACH_ON_CONNECT option. Defaults to false.
identity byte[] The ZMQ_IDENTITY option. Defaults to none.
ipv4Only boolean The ZMQ_IPV4ONLY option. Defaults to true.
linger long The ZMQ_LINGER option. Defaults to -1.
maxMsgSize long The ZMQ_MAXMSGSIZE option. Defaults to -1.
rcvHwm long The ZMQ_RCVHWM option. Defaults to 1000.
receiveBufferSize long The ZMQ_RCVBUF option. Defaults to 0.
receiveTimeOut int The ZMQ_RCVTIMEO option. Defaults to -1.
reconnectIVL long The ZMQ_RECONNECT_IVL option. Defaults to 100.
reconnectIVLMax long The ZMQ_RECONNECT_IVL_MAX option. Defaults to 0.
sendBufferSize long The ZMQ_SNDBUF option. Defaults to 0.
sendTimeOut int The ZMQ_SNDTIMEO option. Defaults to -1.
sndHwm long The ZMQ_SNDHWM option. Defaults to 1000.
tcpKeepAlive int The ZMQ_TCP_KEEPALIVE option. Defaults to -1.
tcpKeepAliveCount long The ZMQ_TCP_KEEPALIVE_CNT option. Defaults to -1.
tcpKeepAliveIdle long The ZMQ_TCP_KEEPALIVE_IDLE option. Defaults to -1.
tcpKeepAliveInterval long The ZMQ_TCP_KEEPALIVE_INTVL option. Defaults to -1.
xpubVerbose boolean The ZMQ_XPUB_VERBOSE option. Defaults to false.